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The CASE
statement performs a switch based on a condition. The basic form is identical to the ternary condition used in many programming languages (CASE WHEN cond THEN a ELSE b END
is equivalent to cond ? a : b
). With a single condition this can be expressed with IF(cond, a, b)
.
CREATE OR REPLACE TABLE integers AS SELECT unnest([1, 2, 3]) AS i;
SELECT i, CASE WHEN i > 2 THEN 1 ELSE 0 END AS test
FROM integers;
-- 1, 2, 3
-- 0, 0, 1
-- this is equivalent to:
SELECT i, IF(i > 2, 1, 0) AS test
FROM integers;
-- 1, 2, 3
-- 0, 0, 1
The WHEN cond THEN expr
part of the CASE
statement can be chained, whenever any of the conditions returns true for a single tuple, the corresponding expression is evaluated and returned.
CREATE OR REPLACE TABLE integers AS SELECT unnest([1, 2, 3]) AS i;
SELECT i, CASE WHEN i = 1 THEN 10 WHEN i = 2 THEN 20 ELSE 0 END AS test
FROM integers;
-- 1, 2, 3
-- 10, 20, 0
The ELSE
part of the CASE
statement is optional. If no else statement is provided and none of the conditions match, the CASE
statement will return NULL
.
CREATE OR REPLACE TABLE integers AS SELECT unnest([1, 2, 3]) AS i;
SELECT i, CASE WHEN i = 1 THEN 10 END AS test
FROM integers;
-- 1, 2, 3
-- 10, NULL, NULL
It is also possible to provide an individual expression after the CASE
but before the WHEN
. When this is done, the CASE
statement is effectively transformed into a switch statement.
CREATE OR REPLACE TABLE integers AS SELECT unnest([1, 2, 3]) AS i;
SELECT i, CASE i WHEN 1 THEN 10 WHEN 2 THEN 20 WHEN 3 THEN 30 END AS test
FROM integers;
-- 1, 2, 3
-- 10, 20, 30
-- this is equivalent to:
SELECT i, CASE WHEN i = 1 THEN 10 WHEN i = 2 THEN 20 WHEN i = 3 THEN 30 END AS test
FROM integers;
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Last modified: 2024-03-19