SQL SELECT statement
SELECT statement
SQL Select statement tells the database to fetch information from a table.
A query or SELECT statement is a command which gives instructions to a database to produce certain information(s) from the table in its memory.
The SELECT command starts with the keyword SELECT followed by a space and a list of comma separated columns. A * character can be used to select all the columns of a table.
The table name comes after the FROM keyword and a white-space.
Syntax:
SELECT *|{[DISTINCT] column|expression [alias]...}
FROM <table_name>;
Parameters:
| Name | Description |
|---|---|
| * | Specifies all the columns of a table. |
| table_name | Name of the table. |
| column | Column names. |
SQL select all columns
To retrieve all the columns from a table, * character is used with SQL SELECT statement.
Example:
The following query displays all the columns of agents table:
Sample table : agents+------------+----------------------+--------------------+------------+-----------------+---------+ | AGENT_CODE | AGENT_NAME | WORKING_AREA | COMMISSION | PHONE_NO | COUNTRY | +------------+----------------------+--------------------+------------+-----------------+---------+ | A007 | Ramasundar | Bangalore | 0.15 | 077-25814763 | | | A003 | Alex | London | 0.13 | 075-12458969 | | | A008 | Alford | New York | 0.12 | 044-25874365 | | | A011 | Ravi Kumar | Bangalore | 0.15 | 077-45625874 | | | A010 | Santakumar | Chennai | 0.14 | 007-22388644 | | | A012 | Lucida | San Jose | 0.12 | 044-52981425 | | | A005 | Anderson | Brisban | 0.13 | 045-21447739 | | | A001 | Subbarao | Bangalore | 0.14 | 077-12346674 | | | A002 | Mukesh | Mumbai | 0.11 | 029-12358964 | | | A006 | McDen | London | 0.15 | 078-22255588 | | | A004 | Ivan | Torento | 0.15 | 008-22544166 | | | A009 | Benjamin | Hampshair | 0.11 | 008-22536178 | | +------------+----------------------+--------------------+------------+-----------------+---------+
SQL Code:
SELECT * FROM agents;
Explanation:
- SELECT *: This command retrieves all columns from the specified table.
- FROM agents: This specifies the table from which to retrieve the data, in this case, the table named "agents".
To achieve the same result, you can use the following statement :
SQL Code:
SELECT agent_code, agent_name, working_area, commission, phone_no
-- Select specific columns: agent_code, agent_name, working_area, commission, phone_no
FROM agents;
-- From the table 'agents'
Explanation:
- SELECT agent_code, agent_name, working_area, commission, phone_no: This line specifies the columns that you want to retrieve data from. It selects the columns 'agent_code', 'agent_name', 'working_area', 'commission', and 'phone_no'.
- FROM agents: This line specifies the table from which you want to retrieve data. In this case, it's the 'agents' table.
Relational Algebra Expression:
Relational Algebra Tree:
Output:
AGENT_CODE AGENT_NAME WORKING_AREA COMMISSION PHONE_NO ---------- ------------------------------ --------------------- ---------- ------------- A003 Alex London .13 075-12458969 A001 Subbarao Bangalore .14 077-12346674 A009 Benjamin Hampshair .11 008-22536178 A007 Ramasundar Bangalore .15 077-25814763 A008 Alford New York .12 044-25874365 A011 Ravi Kumar Bangalore .15 077-45625874 A010 Santakumar Chennai .14 007-22388644 A012 Lucida San Jose .12 044-52981425 A005 Anderson Brisban .13 045-21447739 A002 Mukesh Mumbai .11 029-12358964 A006 McDen London .15 078-22255588 A004 Ivan Torento .15 008-22544166
SQL SELECT: specific columns
The SELECT command can be used to fetch specific column(s) from a table.
Example:
To get all values of agent_name, working_area and commission columns from the agents table, the following SQL statement can be used :
Sample table : agents+------------+----------------------+--------------------+------------+-----------------+---------+ | AGENT_CODE | AGENT_NAME | WORKING_AREA | COMMISSION | PHONE_NO | COUNTRY | +------------+----------------------+--------------------+------------+-----------------+---------+ | A007 | Ramasundar | Bangalore | 0.15 | 077-25814763 | | | A003 | Alex | London | 0.13 | 075-12458969 | | | A008 | Alford | New York | 0.12 | 044-25874365 | | | A011 | Ravi Kumar | Bangalore | 0.15 | 077-45625874 | | | A010 | Santakumar | Chennai | 0.14 | 007-22388644 | | | A012 | Lucida | San Jose | 0.12 | 044-52981425 | | | A005 | Anderson | Brisban | 0.13 | 045-21447739 | | | A001 | Subbarao | Bangalore | 0.14 | 077-12346674 | | | A002 | Mukesh | Mumbai | 0.11 | 029-12358964 | | | A006 | McDen | London | 0.15 | 078-22255588 | | | A004 | Ivan | Torento | 0.15 | 008-22544166 | | | A009 | Benjamin | Hampshair | 0.11 | 008-22536178 | | +------------+----------------------+--------------------+------------+-----------------+---------+
SQL Code:
SELECT agent_name, working_area, commission
-- Select specific columns: agent_name, working_area, commission
FROM agents;
-- From the table 'agents'
Explanation:
- SELECT agent_name, working_area, commission: This line specifies the columns that you want to retrieve data from. It selects the columns 'agent_name', 'working_area', and 'commission'.
- FROM agents: This line specifies the table from which you want to retrieve data. In this case, it's the 'agents' table.
Relational Algebra Expression:
Relational Algebra Tree:
Output:
AGENT_NAME WORKING_AREA COMMISSION ---------------------------------------- ----------------------------------- ---------- Alex London .13 Subbarao Bangalore .14 Benjamin Hampshair .11 Ramasundar Bangalore .15 Alford New York .12 Ravi Kumar Bangalore .15 Santakumar Chennai .14 Lucida San Jose .12 Anderson Brisban .13 Mukesh Mumbai .11 McDen London .15 Ivan Torento .15
SQL SELECT : Using Arithmetic Operators (+, -, *, /) with Employee Salary Calculation
Within SELECT statement you can create an expression with number and field value using arithmetic operators. Here is an example with output:
Sample table : employeesemployee_id first_name last_name email phone_number hire_date job_id salary commission_pct manager_id department_id ----------- ---------- ---------- ---------- ------------ ---------- ---------- ---------- -------------- ---------- ------------- 100 Steven King SKING 515.123.4567 6/17/1987 AD_PRES 24000 90 101 Neena Kochhar NKOCHHAR 515.123.4568 6/18/1987 AD_VP 17000 100 90 102 Lex De Haan LDEHAAN 515.123.4569 6/19/1987 AD_VP 17000 100 90 103 Alexander Hunold AHUNOLD 590.423.4567 6/20/1987 IT_PROG 9000 102 60 104 Bruce Ernst BERNST 590.423.4568 6/21/1987 IT_PROG 6000 103 60 105 David Austin DAUSTIN 590.423.4569 6/22/1987 IT_PROG 4800 103 60 106 Valli Pataballa VPATABAL 590.423.4560 6/23/1987 IT_PROG 4800 103 60 107 Diana Lorentz DLORENTZ 590.423.5567 6/24/1987 IT_PROG 4200 103 60 108 Nancy Greenberg NGREENBE 515.124.4569 6/25/1987 FI_MGR 12000 101 100 109 Daniel Faviet DFAVIET 515.124.4169 6/26/1987 FI_ACCOUNT 9000 108 100 110 John Chen JCHEN 515.124.4269 6/27/1987 FI_ACCOUNT 8200 108 100 111 Ismael Sciarra ISCIARRA 515.124.4369 6/28/1987 FI_ACCOUNT 7700 108 100 112 Jose Manue Urman JMURMAN 515.124.4469 6/29/1987 FI_ACCOUNT 7800 108 100 113 Luis Popp LPOPP 515.124.4567 6/30/1987 FI_ACCOUNT 6900 108 100 114 Den Raphaely DRAPHEAL 515.127.4561 7/1/1987 PU_MAN 11000 100 30 115 Alexander Khoo AKHOO 515.127.4562 7/2/1987 PU_CLERK 3100 114 30 116 Shelli Baida SBAIDA 515.127.4563 7/3/1987 PU_CLERK 2900 114 30 117 Sigal Tobias STOBIAS 515.127.4564 7/4/1987 PU_CLERK 2800 114 30 118 Guy Himuro GHIMURO 515.127.4565 7/5/1987 PU_CLERK 2600 114 30 119 Karen Colmenares KCOLMENA 515.127.4566 7/6/1987 PU_CLERK 2500 114 30 120 Matthew Weiss MWEISS 650.123.1234 7/7/1987 ST_MAN 8000 100 50 121 Adam Fripp AFRIPP 650.123.2234 7/8/1987 ST_MAN 8200 100 50 122 Payam Kaufling PKAUFLIN 650.123.3234 7/9/1987 ST_MAN 7900 100 50 123 Shanta Vollman SVOLLMAN 650.123.4234 7/10/1987 ST_MAN 6500 100 50 124 Kevin Mourgos KMOURGOS 650.123.5234 7/11/1987 ST_MAN 5800 100 50 125 Julia Nayer JNAYER 650.124.1214 7/12/1987 ST_CLERK 3200 120 50 126 Irene Mikkilinen IMIKKILI 650.124.1224 7/13/1987 ST_CLERK 2700 120 50 127 James Landry JLANDRY 650.124.1334 7/14/1987 ST_CLERK 2400 120 50 128 Steven Markle SMARKLE 650.124.1434 7/15/1987 ST_CLERK 2200 120 50 129 Laura Bissot LBISSOT 650.124.5234 7/16/1987 ST_CLERK 3300 121 50 130 Mozhe Atkinson MATKINSO 650.124.6234 7/17/1987 ST_CLERK 2800 121 50 131 James Marlow JAMRLOW 650.124.7234 7/18/1987 ST_CLERK 2500 121 50 132 TJ Olson TJOLSON 650.124.8234 7/19/1987 ST_CLERK 2100 121 50 133 Jason Mallin JMALLIN 650.127.1934 7/20/1987 ST_CLERK 3300 122 50 134 Michael Rogers MROGERS 650.127.1834 7/21/1987 ST_CLERK 2900 122 50 135 Ki Gee KGEE 650.127.1734 7/22/1987 ST_CLERK 2400 122 50 136 Hazel Philtanker HPHILTAN 650.127.1634 7/23/1987 ST_CLERK 2200 122 50 137 Renske Ladwig RLADWIG 650.121.1234 7/24/1987 ST_CLERK 3600 123 50 138 Stephen Stiles SSTILES 650.121.2034 7/25/1987 ST_CLERK 3200 123 50 139 John Seo JSEO 650.121.2019 7/26/1987 ST_CLERK 2700 123 50 140 Joshua Patel JPATEL 650.121.1834 7/27/1987 ST_CLERK 2500 123 50 141 Trenna Rajs TRAJS 650.121.8009 7/28/1987 ST_CLERK 3500 124 50 142 Curtis Davies CDAVIES 650.121.2994 7/29/1987 ST_CLERK 3100 124 50 143 Randall Matos RMATOS 650.121.2874 7/30/1987 ST_CLERK 2600 124 50 144 Peter Vargas PVARGAS 650.121.2004 7/31/1987 ST_CLERK 2500 124 50 145 John Russell JRUSSEL 011.44.1344. 8/1/1987 SA_MAN 14000 0.4 100 80 146 Karen Partners KPARTNER 011.44.1344. 8/2/1987 SA_MAN 13500 0.3 100 80 147 Alberto Errazuriz AERRAZUR 011.44.1344. 8/3/1987 SA_MAN 12000 0.3 100 80 148 Gerald Cambrault GCAMBRAU 011.44.1344. 8/4/1987 SA_MAN 11000 0.3 100 80 149 Eleni Zlotkey EZLOTKEY 011.44.1344. 8/5/1987 SA_MAN 10500 0.2 100 80 150 Peter Tucker PTUCKER 011.44.1344. 8/6/1987 SA_REP 10000 0.3 145 80 151 David Bernstein DBERNSTE 011.44.1344. 8/7/1987 SA_REP 9500 0.25 145 80 152 Peter Hall PHALL 011.44.1344. 8/8/1987 SA_REP 9000 0.25 145 80 153 Christophe Olsen COLSEN 011.44.1344. 8/9/1987 SA_REP 8000 0.2 145 80 154 Nanette Cambrault NCAMBRAU 011.44.1344. 8/10/1987 SA_REP 7500 0.2 145 80 155 Oliver Tuvault OTUVAULT 011.44.1344. 8/11/1987 SA_REP 7000 0.15 145 80 156 Janette King JKING 011.44.1345. 8/12/1987 SA_REP 10000 0.35 146 80 157 Patrick Sully PSULLY 011.44.1345. 8/13/1987 SA_REP 9500 0.35 146 80 158 Allan McEwen AMCEWEN 011.44.1345. 8/14/1987 SA_REP 9000 0.35 146 80 159 Lindsey Smith LSMITH 011.44.1345. 8/15/1987 SA_REP 8000 0.3 146 80 160 Louise Doran LDORAN 011.44.1345. 8/16/1987 SA_REP 7500 0.3 146 80 161 Sarath Sewall SSEWALL 011.44.1345. 8/17/1987 SA_REP 7000 0.25 146 80 162 Clara Vishney CVISHNEY 011.44.1346. 8/18/1987 SA_REP 10500 0.25 147 80 163 Danielle Greene DGREENE 011.44.1346. 8/19/1987 SA_REP 9500 0.15 147 80 164 Mattea Marvins MMARVINS 011.44.1346. 8/20/1987 SA_REP 7200 0.1 147 80 165 David Lee DLEE 011.44.1346. 8/21/1987 SA_REP 6800 0.1 147 80 166 Sundar Ande SANDE 011.44.1346. 8/22/1987 SA_REP 6400 0.1 147 80 167 Amit Banda ABANDA 011.44.1346. 8/23/1987 SA_REP 6200 0.1 147 80 168 Lisa Ozer LOZER 011.44.1343. 8/24/1987 SA_REP 11500 0.25 148 80 169 Harrison Bloom HBLOOM 011.44.1343. 8/25/1987 SA_REP 10000 0.2 148 80 170 Tayler Fox TFOX 011.44.1343. 8/26/1987 SA_REP 9600 0.2 148 80 171 William Smith WSMITH 011.44.1343. 8/27/1987 SA_REP 7400 0.15 148 80 172 Elizabeth Bates EBATES 011.44.1343. 8/28/1987 SA_REP 7300 0.15 148 80 173 Sundita Kumar SKUMAR 011.44.1343. 8/29/1987 SA_REP 6100 0.1 148 80 174 Ellen Abel EABEL 011.44.1644. 8/30/1987 SA_REP 11000 0.3 149 80 175 Alyssa Hutton AHUTTON 011.44.1644. 8/31/1987 SA_REP 8800 0.25 149 80 176 Jonathon Taylor JTAYLOR 011.44.1644. 9/1/1987 SA_REP 8600 0.2 149 80 177 Jack Livingston JLIVINGS 011.44.1644. 9/2/1987 SA_REP 8400 0.2 149 80 178 Kimberely Grant KGRANT 011.44.1644. 9/3/1987 SA_REP 7000 0.15 149 179 Charles Johnson CJOHNSON 011.44.1644. 9/4/1987 SA_REP 6200 0.1 149 80 180 Winston Taylor WTAYLOR 650.507.9876 9/5/1987 SH_CLERK 3200 120 50 181 Jean Fleaur JFLEAUR 650.507.9877 9/6/1987 SH_CLERK 3100 120 50 182 Martha Sullivan MSULLIVA 650.507.9878 9/7/1987 SH_CLERK 2500 120 50 183 Girard Geoni GGEONI 650.507.9879 9/8/1987 SH_CLERK 2800 120 50 184 Nandita Sarchand NSARCHAN 650.509.1876 9/9/1987 SH_CLERK 4200 121 50 185 Alexis Bull ABULL 650.509.2876 9/10/1987 SH_CLERK 4100 121 50 186 Julia Dellinger JDELLING 650.509.3876 9/11/1987 SH_CLERK 3400 121 50 187 Anthony Cabrio ACABRIO 650.509.4876 9/12/1987 SH_CLERK 3000 121 50 188 Kelly Chung KCHUNG 650.505.1876 9/13/1987 SH_CLERK 3800 122 50 189 Jennifer Dilly JDILLY 650.505.2876 9/14/1987 SH_CLERK 3600 122 50 190 Timothy Gates TGATES 650.505.3876 9/15/1987 SH_CLERK 2900 122 50 191 Randall Perkins RPERKINS 650.505.4876 9/16/1987 SH_CLERK 2500 122 50 192 Sarah Bell SBELL 650.501.1876 9/17/1987 SH_CLERK 4000 123 50 193 Britney Everett BEVERETT 650.501.2876 9/18/1987 SH_CLERK 3900 123 50 194 Samuel McCain SMCCAIN 650.501.3876 9/19/1987 SH_CLERK 3200 123 50 195 Vance Jones VJONES 650.501.4876 9/20/1987 SH_CLERK 2800 123 50 196 Alana Walsh AWALSH 650.507.9811 9/21/1987 SH_CLERK 3100 124 50 197 Kevin Feeney KFEENEY 650.507.9822 9/22/1987 SH_CLERK 3000 124 50 198 Donald OConnell DOCONNEL 650.507.9833 9/23/1987 SH_CLERK 2600 124 50 199 Douglas Grant DGRANT 650.507.9844 9/24/1987 SH_CLERK 2600 124 50 200 Jennifer Whalen JWHALEN 515.123.4444 9/25/1987 AD_ASST 4400 101 10 201 Michael Hartstein MHARTSTE 515.123.5555 9/26/1987 MK_MAN 13000 100 20 202 Pat Fay PFAY 603.123.6666 9/27/1987 MK_REP 6000 201 20 203 Susan Mavris SMAVRIS 515.123.7777 9/28/1987 HR_REP 6500 101 40 204 Hermann Baer HBAER 515.123.8888 9/29/1987 PR_REP 10000 101 70 205 Shelley Higgins SHIGGINS 515.123.8080 9/30/1987 AC_MGR 12000 101 110 206 William Gietz WGIETZ 515.123.8181 10/1/1987 AC_ACCOUNT 8300 205 110
SQL Code:
SELECT first_name, last_name, salary, (12*salary + 400)
-- Select specific columns: first_name, last_name, salary, and a calculated expression (12*salary + 400)
FROM employees;
-- From the table 'employees'
Explanation:
- SELECT first_name, last_name, salary, (12*salary + 400): This line specifies the columns that you want to retrieve data from. It selects the columns 'first_name', 'last_name', and 'salary' directly from the 'employees' table. Additionally, it calculates a new value using the expression (12*salary + 400). This expression multiplies the 'salary' by 12, adds 400 to the result, and returns the final value.
- FROM employees: This line specifies the table from which you want to retrieve data. In this case, it's the 'employees' table.
Relational Algebra Expression:
Relational Algebra Tree:
Output:
FIRST_NAME LAST_NAME SALARY (12*SALARY+400) -------------------- ------------------------- ---------- --------------- Steven King 24000 288400 Neena Kochhar 17000 204400 Lex De Haan 17000 204400 Alexander Hunold 9000 108400 Bruce Ernst 6000 72400 David Austin 4800 58000 Valli Pataballa 4800 58000 Diana Lorentz 4200 50800 Nancy Greenberg 12008 144496 Daniel Faviet 9000 108400 John Chen 8200 98800 Ismael Sciarra 7700 92800 ..................................................
SQL SELECT: Using Column Aliases for Employee Details Retrieval
- To renames a column heading temporarily for a particular SQL query you can use column aliases.
- There can be an optional AS keyword between the column name and alias
- It requires double quotation marks if the column name string contains
spaces or special characters or if it is case sensitive.
See the following examples using AS keyword and without AS Keyword.
Sample table : employeesemployee_id first_name last_name email phone_number hire_date job_id salary commission_pct manager_id department_id ----------- ---------- ---------- ---------- ------------ ---------- ---------- ---------- -------------- ---------- ------------- 100 Steven King SKING 515.123.4567 6/17/1987 AD_PRES 24000 90 101 Neena Kochhar NKOCHHAR 515.123.4568 6/18/1987 AD_VP 17000 100 90 102 Lex De Haan LDEHAAN 515.123.4569 6/19/1987 AD_VP 17000 100 90 103 Alexander Hunold AHUNOLD 590.423.4567 6/20/1987 IT_PROG 9000 102 60 104 Bruce Ernst BERNST 590.423.4568 6/21/1987 IT_PROG 6000 103 60 105 David Austin DAUSTIN 590.423.4569 6/22/1987 IT_PROG 4800 103 60 106 Valli Pataballa VPATABAL 590.423.4560 6/23/1987 IT_PROG 4800 103 60 107 Diana Lorentz DLORENTZ 590.423.5567 6/24/1987 IT_PROG 4200 103 60 108 Nancy Greenberg NGREENBE 515.124.4569 6/25/1987 FI_MGR 12000 101 100 109 Daniel Faviet DFAVIET 515.124.4169 6/26/1987 FI_ACCOUNT 9000 108 100 110 John Chen JCHEN 515.124.4269 6/27/1987 FI_ACCOUNT 8200 108 100 111 Ismael Sciarra ISCIARRA 515.124.4369 6/28/1987 FI_ACCOUNT 7700 108 100 112 Jose Manue Urman JMURMAN 515.124.4469 6/29/1987 FI_ACCOUNT 7800 108 100 113 Luis Popp LPOPP 515.124.4567 6/30/1987 FI_ACCOUNT 6900 108 100 114 Den Raphaely DRAPHEAL 515.127.4561 7/1/1987 PU_MAN 11000 100 30 115 Alexander Khoo AKHOO 515.127.4562 7/2/1987 PU_CLERK 3100 114 30 116 Shelli Baida SBAIDA 515.127.4563 7/3/1987 PU_CLERK 2900 114 30 117 Sigal Tobias STOBIAS 515.127.4564 7/4/1987 PU_CLERK 2800 114 30 118 Guy Himuro GHIMURO 515.127.4565 7/5/1987 PU_CLERK 2600 114 30 119 Karen Colmenares KCOLMENA 515.127.4566 7/6/1987 PU_CLERK 2500 114 30 120 Matthew Weiss MWEISS 650.123.1234 7/7/1987 ST_MAN 8000 100 50 121 Adam Fripp AFRIPP 650.123.2234 7/8/1987 ST_MAN 8200 100 50 122 Payam Kaufling PKAUFLIN 650.123.3234 7/9/1987 ST_MAN 7900 100 50 123 Shanta Vollman SVOLLMAN 650.123.4234 7/10/1987 ST_MAN 6500 100 50 124 Kevin Mourgos KMOURGOS 650.123.5234 7/11/1987 ST_MAN 5800 100 50 125 Julia Nayer JNAYER 650.124.1214 7/12/1987 ST_CLERK 3200 120 50 126 Irene Mikkilinen IMIKKILI 650.124.1224 7/13/1987 ST_CLERK 2700 120 50 127 James Landry JLANDRY 650.124.1334 7/14/1987 ST_CLERK 2400 120 50 128 Steven Markle SMARKLE 650.124.1434 7/15/1987 ST_CLERK 2200 120 50 129 Laura Bissot LBISSOT 650.124.5234 7/16/1987 ST_CLERK 3300 121 50 130 Mozhe Atkinson MATKINSO 650.124.6234 7/17/1987 ST_CLERK 2800 121 50 131 James Marlow JAMRLOW 650.124.7234 7/18/1987 ST_CLERK 2500 121 50 132 TJ Olson TJOLSON 650.124.8234 7/19/1987 ST_CLERK 2100 121 50 133 Jason Mallin JMALLIN 650.127.1934 7/20/1987 ST_CLERK 3300 122 50 134 Michael Rogers MROGERS 650.127.1834 7/21/1987 ST_CLERK 2900 122 50 135 Ki Gee KGEE 650.127.1734 7/22/1987 ST_CLERK 2400 122 50 136 Hazel Philtanker HPHILTAN 650.127.1634 7/23/1987 ST_CLERK 2200 122 50 137 Renske Ladwig RLADWIG 650.121.1234 7/24/1987 ST_CLERK 3600 123 50 138 Stephen Stiles SSTILES 650.121.2034 7/25/1987 ST_CLERK 3200 123 50 139 John Seo JSEO 650.121.2019 7/26/1987 ST_CLERK 2700 123 50 140 Joshua Patel JPATEL 650.121.1834 7/27/1987 ST_CLERK 2500 123 50 141 Trenna Rajs TRAJS 650.121.8009 7/28/1987 ST_CLERK 3500 124 50 142 Curtis Davies CDAVIES 650.121.2994 7/29/1987 ST_CLERK 3100 124 50 143 Randall Matos RMATOS 650.121.2874 7/30/1987 ST_CLERK 2600 124 50 144 Peter Vargas PVARGAS 650.121.2004 7/31/1987 ST_CLERK 2500 124 50 145 John Russell JRUSSEL 011.44.1344. 8/1/1987 SA_MAN 14000 0.4 100 80 146 Karen Partners KPARTNER 011.44.1344. 8/2/1987 SA_MAN 13500 0.3 100 80 147 Alberto Errazuriz AERRAZUR 011.44.1344. 8/3/1987 SA_MAN 12000 0.3 100 80 148 Gerald Cambrault GCAMBRAU 011.44.1344. 8/4/1987 SA_MAN 11000 0.3 100 80 149 Eleni Zlotkey EZLOTKEY 011.44.1344. 8/5/1987 SA_MAN 10500 0.2 100 80 150 Peter Tucker PTUCKER 011.44.1344. 8/6/1987 SA_REP 10000 0.3 145 80 151 David Bernstein DBERNSTE 011.44.1344. 8/7/1987 SA_REP 9500 0.25 145 80 152 Peter Hall PHALL 011.44.1344. 8/8/1987 SA_REP 9000 0.25 145 80 153 Christophe Olsen COLSEN 011.44.1344. 8/9/1987 SA_REP 8000 0.2 145 80 154 Nanette Cambrault NCAMBRAU 011.44.1344. 8/10/1987 SA_REP 7500 0.2 145 80 155 Oliver Tuvault OTUVAULT 011.44.1344. 8/11/1987 SA_REP 7000 0.15 145 80 156 Janette King JKING 011.44.1345. 8/12/1987 SA_REP 10000 0.35 146 80 157 Patrick Sully PSULLY 011.44.1345. 8/13/1987 SA_REP 9500 0.35 146 80 158 Allan McEwen AMCEWEN 011.44.1345. 8/14/1987 SA_REP 9000 0.35 146 80 159 Lindsey Smith LSMITH 011.44.1345. 8/15/1987 SA_REP 8000 0.3 146 80 160 Louise Doran LDORAN 011.44.1345. 8/16/1987 SA_REP 7500 0.3 146 80 161 Sarath Sewall SSEWALL 011.44.1345. 8/17/1987 SA_REP 7000 0.25 146 80 162 Clara Vishney CVISHNEY 011.44.1346. 8/18/1987 SA_REP 10500 0.25 147 80 163 Danielle Greene DGREENE 011.44.1346. 8/19/1987 SA_REP 9500 0.15 147 80 164 Mattea Marvins MMARVINS 011.44.1346. 8/20/1987 SA_REP 7200 0.1 147 80 165 David Lee DLEE 011.44.1346. 8/21/1987 SA_REP 6800 0.1 147 80 166 Sundar Ande SANDE 011.44.1346. 8/22/1987 SA_REP 6400 0.1 147 80 167 Amit Banda ABANDA 011.44.1346. 8/23/1987 SA_REP 6200 0.1 147 80 168 Lisa Ozer LOZER 011.44.1343. 8/24/1987 SA_REP 11500 0.25 148 80 169 Harrison Bloom HBLOOM 011.44.1343. 8/25/1987 SA_REP 10000 0.2 148 80 170 Tayler Fox TFOX 011.44.1343. 8/26/1987 SA_REP 9600 0.2 148 80 171 William Smith WSMITH 011.44.1343. 8/27/1987 SA_REP 7400 0.15 148 80 172 Elizabeth Bates EBATES 011.44.1343. 8/28/1987 SA_REP 7300 0.15 148 80 173 Sundita Kumar SKUMAR 011.44.1343. 8/29/1987 SA_REP 6100 0.1 148 80 174 Ellen Abel EABEL 011.44.1644. 8/30/1987 SA_REP 11000 0.3 149 80 175 Alyssa Hutton AHUTTON 011.44.1644. 8/31/1987 SA_REP 8800 0.25 149 80 176 Jonathon Taylor JTAYLOR 011.44.1644. 9/1/1987 SA_REP 8600 0.2 149 80 177 Jack Livingston JLIVINGS 011.44.1644. 9/2/1987 SA_REP 8400 0.2 149 80 178 Kimberely Grant KGRANT 011.44.1644. 9/3/1987 SA_REP 7000 0.15 149 179 Charles Johnson CJOHNSON 011.44.1644. 9/4/1987 SA_REP 6200 0.1 149 80 180 Winston Taylor WTAYLOR 650.507.9876 9/5/1987 SH_CLERK 3200 120 50 181 Jean Fleaur JFLEAUR 650.507.9877 9/6/1987 SH_CLERK 3100 120 50 182 Martha Sullivan MSULLIVA 650.507.9878 9/7/1987 SH_CLERK 2500 120 50 183 Girard Geoni GGEONI 650.507.9879 9/8/1987 SH_CLERK 2800 120 50 184 Nandita Sarchand NSARCHAN 650.509.1876 9/9/1987 SH_CLERK 4200 121 50 185 Alexis Bull ABULL 650.509.2876 9/10/1987 SH_CLERK 4100 121 50 186 Julia Dellinger JDELLING 650.509.3876 9/11/1987 SH_CLERK 3400 121 50 187 Anthony Cabrio ACABRIO 650.509.4876 9/12/1987 SH_CLERK 3000 121 50 188 Kelly Chung KCHUNG 650.505.1876 9/13/1987 SH_CLERK 3800 122 50 189 Jennifer Dilly JDILLY 650.505.2876 9/14/1987 SH_CLERK 3600 122 50 190 Timothy Gates TGATES 650.505.3876 9/15/1987 SH_CLERK 2900 122 50 191 Randall Perkins RPERKINS 650.505.4876 9/16/1987 SH_CLERK 2500 122 50 192 Sarah Bell SBELL 650.501.1876 9/17/1987 SH_CLERK 4000 123 50 193 Britney Everett BEVERETT 650.501.2876 9/18/1987 SH_CLERK 3900 123 50 194 Samuel McCain SMCCAIN 650.501.3876 9/19/1987 SH_CLERK 3200 123 50 195 Vance Jones VJONES 650.501.4876 9/20/1987 SH_CLERK 2800 123 50 196 Alana Walsh AWALSH 650.507.9811 9/21/1987 SH_CLERK 3100 124 50 197 Kevin Feeney KFEENEY 650.507.9822 9/22/1987 SH_CLERK 3000 124 50 198 Donald OConnell DOCONNEL 650.507.9833 9/23/1987 SH_CLERK 2600 124 50 199 Douglas Grant DGRANT 650.507.9844 9/24/1987 SH_CLERK 2600 124 50 200 Jennifer Whalen JWHALEN 515.123.4444 9/25/1987 AD_ASST 4400 101 10 201 Michael Hartstein MHARTSTE 515.123.5555 9/26/1987 MK_MAN 13000 100 20 202 Pat Fay PFAY 603.123.6666 9/27/1987 MK_REP 6000 201 20 203 Susan Mavris SMAVRIS 515.123.7777 9/28/1987 HR_REP 6500 101 40 204 Hermann Baer HBAER 515.123.8888 9/29/1987 PR_REP 10000 101 70 205 Shelley Higgins SHIGGINS 515.123.8080 9/30/1987 AC_MGR 12000 101 110 206 William Gietz WGIETZ 515.123.8181 10/1/1987 AC_ACCOUNT 8300 205 110
SQL Code:
SELECT first_name AS "First Name", last_name AS "Last Name", salary AS "Salary"
-- Select specific columns: first_name, last_name, salary, with aliases for column names
FROM employees;
-- From the table 'employees'
Explanation:
- SELECT first_name AS "First Name", last_name AS "Last Name", salary AS "Salary": This line specifies the columns that you want to retrieve data from. It selects the columns 'first_name', 'last_name', and 'salary' from the 'employees' table. Additionally, it uses the AS keyword to provide aliases for the column names. The aliases are "First Name" for 'first_name', "Last Name" for 'last_name', and "Salary" for 'salary'.
- FROM employees: This line specifies the table from which you want to retrieve data. In this case, it's the 'employees' table.
Output:
First Name Last Name Salary -------------------- ------------------------- ---------- Steven King 24000 Neena Kochhar 17000 Lex De Haan 17000 Alexander Hunold 9000 Bruce Ernst 6000 David Austin 4800 Valli Pataballa 4800 Diana Lorentz 4200 Nancy Greenberg 12008 Daniel Faviet 9000 John Chen 8200 Ismael Sciarra 7700 Jose Manuel Urman 7800 Luis Popp 6900 Den Raphaely 11000 Alexander Khoo 3100 Shelli Baida 2900 Sigal Tobias 2800 ...................................
SQL Code:
SELECT first_name "First Name", last_name "Last Name", salary "Salary"
-- Select specific columns: first_name, last_name, salary, without using the AS keyword for aliases
FROM employees;
-- From the table 'employees'
Explanation:
- SELECT first_name "First Name", last_name "Last Name", salary "Salary": This line specifies the columns that you want to retrieve data from. It selects the columns 'first_name', 'last_name', and 'salary' from the 'employees' table. Additionally, it uses double quotes to provide aliases for the column names. The aliases are "First Name" for 'first_name', "Last Name" for 'last_name', and "Salary" for 'salary'.
- FROM employees: This line specifies the table from which you want to retrieve data. In this case, it's the 'employees' table.
Output:
First Name Last Name Salary -------------------- ------------------------- ---------- Steven King 24000 Neena Kochhar 17000 Lex De Haan 17000 Alexander Hunold 9000 Bruce Ernst 6000 David Austin 4800 Valli Pataballa 4800 Diana Lorentz 4200 Nancy Greenberg 12008 Daniel Faviet 9000 John Chen 8200 Ismael Sciarra 7700 Jose Manuel Urman 7800 Luis Popp 6900 Den Raphaely 11000 Alexander Khoo 3100 Shelli Baida 2900 Sigal Tobias 2800 Guy Himuro 2600 ...........................................
SQL SELECT statement with NULL values
Before storing a value in any field of a table, a NULL value can be stored; later that NULL value can be replaced with the desired value. When a field value is NULL it means that the database assigned nothing (not even a zero "0" or blank " " ), in that field for that row.
Since the NULL represents an unknown or inapplicable value, it can’t be compared using the AND / OR logical operators. The special operator ‘IS’ is used with the keyword ‘NULL’ to locate ‘NULL’ values. NULL can be assigned to both types of fields i.e. numeric or character type.
Example:
Sample table: foods+---------+--------------+-----------+------------+ | ITEM_ID | ITEM_NAME | ITEM_UNIT | COMPANY_ID | +---------+--------------+-----------+------------+ | 1 | Chex Mix | Pcs | 16 | | 6 | Cheez-It | Pcs | 15 | | 2 | BN Biscuit | Pcs | 15 | | 3 | Mighty Munch | Pcs | 17 | | 4 | Pot Rice | Pcs | 15 | | 5 | Jaffa Cakes | Pcs | 18 | | 7 | Salt n Shake | Pcs | | +---------+--------------+-----------+------------+
To get data of all columns from the foods table with the following condition -
1. company_id column must contain NULL value,
the following SQL statement can be used:
SQL Code:
SELECT * FROM foods
-- Select all columns
WHERE company_id IS NULL;
-- Filter the results to only include rows where the company_id is NULL
Explanation:
- SELECT * FROM foods: This line specifies the columns that you want to retrieve data from. The asterisk (*) is a wildcard symbol that represents all columns in the table. So, this query selects all columns from the 'foods' table.
- WHERE company_id IS NULL: This line specifies a condition for filtering the results. It filters the results to only include rows where the value in the 'company_id' column is NULL.
Relational Algebra Expression:
Relational Algebra Tree:
Output:
ITEM_ID ITEM_NAME ITEM_UNIT COMPANY_ID -------- ------------------------- --------- ---------- 7 Salt n Shake Pcs
In the next session, we have discussed Select with distinct and SQL select with distinct on multiple columns in detail.
Check out our 1000+ SQL Exercises with solution and explanation to improve your skills.