SQL: WHERE clause

When retrieving data from a single table or by joining data from multiple tables, a condition is specified using the SQL WHERE clause. If the given condition is satisfied, then only it returns a specific value from the table. The WHERE clause should be used to filter the records and only retrieve those that are required.

Syntax:

SELECT column_names
FROM table_name
WHERE conditions;

The SELECT clause specifies the columns to be returned from the table(s), the WHERE clause contains the conditions that must evaluate to true for a row to be returned as a result.

Operators that can be used with where clause:

Operator	Description
>	Greater Than
>=	Greater than or Equal to
<	Less Than
<=	Less than or Equal to
=	Equal to
<>	Not Equal to
BETWEEN	In an inclusive Range
LIKE	Search for a pattern
IN	To specify multiple possible values for a column

Example:

Consider the PRODUCTS table having the following records −

ID	ITEM	QUANTITY	PRICE_PER_ITEM
1	Chair	67	850.00
2	Ball	12	600.00
3	Jars	9	500.00

• Query to select an item based on a condition:

SELECT ID, 
    ITEM, 
    QUANTITY, 
    PRICE_PER_ITEM 
    FROM PRODUCTS WHERE ID = 3;

Output:

ID	ITEM	QUANTITY	PRICE_PER_ITEM
3	Jars	9	500.00

• Query to fetch ITEM and QUANTITY of PRODUCTS with PRICE greater than 500.00

SELECT ID, 
    ITEM, 
    QUANTITY
    FROM PRODUCTS WHERE PRICE_PER_ITEM > 500.00;

Output:

ID	ITEM	QUANTITY
1	Chair	67
2	Ball	12

• Query to fetch PRICE for chair:

SELECT ID,ITEM,PRICE_PER_ITEM
    FROM PRODUCTS WHERE ITEM = "Chair";

Output:

ID	ITEM	PRICE_PER_ITEM
1	Chair	850.00

Note: multiple conditions in the where clause can be used as per the requirements.

Note: also read about DCL Commands: GRANT and REVOKE

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