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Mysql – SQL to query a table only if the table contains data

This query below is running but I would like to add this extra condition; run this query only if there is data in the table STAGE.LAB.DATA.
I tried CASE and IF THEN, but I can’t get it to work. Please help. What syntax should be added? Thanks

SELECT *
 FROM
 ( SELECT EXISTS ( SELECT 1 FROM STAGE.LAB.DATA A
  WHERE (A.HOT_TEMP_VALUE >= 118 AND A.HOT_TEMP_VALUE <= 122) ) AS result)
   WHERE RESULT !='TRUE';

IF
 SELECT COUNT(*) FROM STAGE.LAB.DATA >1
 THEN
 SELECT *
 FROM
 ( SELECT EXISTS ( SELECT 1 FROM STAGE.LAB.DATA A
 WHERE (A.HOT_TEMP_VALUE >= 118 AND A.HOT_TEMP_VALUE <= 122) ) AS result)
 WHERE RESULT !='TRUE';
 ELSE
  END IF
Tags:

2

Answers


  1. 0

    In order to use a query result as a value, you have to put it in parentheses:

    IF (SELECT COUNT(*) FROM STAGE.LAB.DATA) >= 1
THEN 
    ...
END IF

    IF statements can only be used in stored programs. In an ordinary query, you can use WHERE clause:

    SELECT *
FROM otherTable
WHERE EXISTS (SELECT 1 FROM STAGE.LAB.DATA)

    This will return an empty result if there’s nothing in STAGE.LAB.DATA.

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  2. 0 
    IF EXISTS (SELECT NULL FROM STAGE.LAB.DATA) THEN 
  ...
END IF

    SELECT ...
  ...
WHERE EXISTS (SELECT NULL FROM STAGE.LAB.DATA)
  ...

    EXISTS stops table scanning after first matched row is found. Rather than COUNT()..

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