4. SQL Statements : SELECT : SELECT Statement Clauses : WHERE Clause
 
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WHERE Clause
The WHERE clause specifies criteria that restrict the contents of the results table. You can test for simple relationships or, using subselects, for relationships between a column and a set of columns.
Using a simple WHERE clause, the contents of the results table can be restricted, as follows:
Comparisons:
SELECT ename FROM employee_dim
    WHERE manager = 'Al Obidinski';
SELECT emp_name FROM employee_dim
    WHERE salary > 50000;
Ranges:
SELECT ordnum FROM orders
       WHERE odate BETWEEN DATE('2014-01-01') AND CURRENT_DATE;
Set membership:
SELECT * FROM orders
       WHERE partno IN ('123-45', '678-90');
Pattern matching:
SELECT * FROM employee_dim
       WHERE emp_name LIKE 'A%';
Nulls:
SELECT emp_name FROM employee_dim
       WHERE dept_no IS NULL;
Combined restrictions using logical operators:
SELECT emp_name FROM employee_dim
       WHERE dept_no IS NULL AND
       hiredate = CURRENT_DATE;
Note:  Aggregate functions cannot appear in a WHERE clause.
More information:
Predicates in SQL