CASE
Definition
The CASE
function allows you to perform conditional statements in BigQuery. This is a more complex implementation of IF
.
Syntax
CASE expr
WHEN expr_to_match THEN result
[...]
[ELSE else_result]
END
SELECT
colour,
CASE WHEN colour IN ('blue', 'red', 'yellow') THEN true ELSE false END AS primary_colour
FROM
(
SELECT
'blue' AS colour
UNION ALL
( SELECT
'pink' AS colour)
UNION ALL
( SELECT
'black' AS colour)
) AS table_3
Practical Info
else_result
, then the query will return NULL
if not matched to the result
result
and else_result
must be coercible to a common supertype. Common Questions
How to create multiple 'THEN' clauses for a case statement?
To add multiple expression -> result pairings, simply add another WHEN ... THEN
clause (without commas) to your function.
Using the example data above, we could use the following query to identify which are the primary colours:
CASE WHEN colour ='blue' THEN true
WHEN colour = 'red' THEN true
WHEN colour = 'yellow' then true
ELSE false
END AS primary_colour
How to compare strings ignoring case?
To account for strings being of different cases, we can use UPPER
and LOWER
to standardise all of the cases in both our expressions to match, and the match criteria.
Using the data above, we could modify our case statement as follows:
CASE
WHEN UPPER(colour) IN ('BLUE', 'RED', 'YELLOW') THEN true
ELSE false
END AS primary_colour
How to compare dates using a case statement?
As long as your expressions are of the right type you can use comparison operators (e.g. >
, <
, >=
) to compare dates:
CASE
WHEN date_col BETWEEN '2020-10-01' and '2021-09-30' THEN 'FY 2021'
WHEN date_col<'2020-10-01' then 'pre FY 2021'
END fiscal_date
Note: BETWEEN
is inclusive so it will return true for both 2020-10-01 AND 2021-09-30.
SELECT
date_col,
CASE WHEN (date_col BETWEEN '2020-10-01' AND '2021-09-30') THEN 'FY 2021' WHEN (date_col < '2020-10-01') THEN 'pre FY 2021' END AS fiscal_date
FROM
(
SELECT
'2020-10-01' AS date_col
UNION ALL
( SELECT
'2021-09-30' AS date_col)
UNION ALL
( SELECT
'2019-10-01' AS date_col)
) AS table_3
How to Group By / Aggregate by a Case function
To group by the results of a CASE
function, just make sure you add the name of the column to your GROUP BY
clause.
SELECT
SUM(number),
CASE WHEN city IN ('New York', 'Miami') THEN 'East' ELSE 'West' END AS Region
FROM
(
SELECT
2 AS number,
'New York' AS city
UNION ALL
( SELECT
4 AS number,
'Los Angeles' AS city)
UNION ALL
( SELECT
(-3) AS number,
'Miami' AS city)
) AS table_3
GROUP BY
Region
To aggregate by a case column, make sure your results are numbers:
SELECT
SUM(CASE WHEN city IN ('New York', 'Miami') THEN number ELSE 0 END) AS east_total,
SUM(CASE WHEN city IN ('Los Angeles') THEN number ELSE 0 END) AS west_total
FROM
(
SELECT
2 AS number,
'New York' AS city
UNION ALL
( SELECT
4 AS number,
'Los Angeles' AS city)
UNION ALL
( SELECT
(-3) AS number,
'Miami' AS city)
) AS table_3
Troubleshooting Common Errors
Type mismatch for operands of = operator: number and string.
This happens when your conditional expression is invalid. For example:
CASE WHEN number_column = 'string' ....
You can resolve this by making sure your condition column and criteria are compatible types:
CASE WHEN CAST(number_column as STRING) = 'string' ...
Case expression returns with mixed types are not supported.
This error occurs when your result types are different. In this example returning 1 in one case and 'hello' in another won't work.
CASE WHEN (CAST(bq.Avg_monthly_searches AS STRING) = 'total') THEN 1 ELSE 'hello' END
To resolve this, make sure your result types are compatible and coercible.
CASE WHEN (CAST(bq.Avg_monthly_searches AS STRING) = 'total') THEN '1' ELSE 'hello' END