How Can I Perform Conditional Logic in SQL SELECT Statements?
Jan 22, 2025 pm 03:16 PMConditional Logic within SQL SELECT Statements: A Comprehensive Guide
SQL often requires conditional logic within SELECT
statements to modify or filter data. The CASE
statement provides a versatile solution, supported across numerous SQL dialects.
To mimic an IF...THEN
structure in a SELECT
query, employ the CASE
statement as shown below:
SELECT CAST( CASE WHEN condition1 OR condition2 THEN value_if_true ELSE value_if_false END AS data_type) AS new_column, * FROM table_name;
Here's a breakdown of the syntax:
condition1
andcondition2
: The conditions to evaluate.value_if_true
andvalue_if_false
: The values returned depending on whether the conditions are true or false.data_type
: The data type of thenew_column
result.table_name
: The table from which data is selected.
For instance, to add a Saleable
column to a Product
table, indicating product availability based on Obsolete
and InStock
status:
SELECT CAST( CASE WHEN Obsolete = 'N' OR InStock = 'Y' THEN 1 ELSE 0 END AS bit) AS Saleable, * FROM Product;
A simplified version, omitting CAST
, yields an integer result:
SELECT CASE WHEN Obsolete = 'N' OR InStock = 'Y' THEN 1 ELSE 0 END AS Saleable, * FROM Product;
CASE
statements can be nested or integrated into aggregate functions. Moreover, SQL Server 2012 introduced the IIF
statement, offering an alternative concise syntax:
SELECT IIF(Obsolete = 'N' OR InStock = 'Y', 1, 0) AS Saleable, * FROM Product;
This simplifies conditional logic within your SELECT
statements, providing flexibility and efficiency in data manipulation.
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