What's the difference between DECLARE and SET using SQL (or more specifically MySQL)?
Both can set variables it seems. I have read the MySQL docs and I did not understand the difference between the two.
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6`DECLARE` declares it and `SET` initializes it. – Tim Schmelter Nov 19 '13 at 14:07
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[link](http://stackoverflow.com/questions/11754781/declare-a-variable-in-mysql) Similar Post – Youbaraj Sharma Nov 19 '13 at 14:11
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@TimSchmelter So both DECLARE and SET are needed unless you use "DEFAULT" with DECLARE? – C H Nov 19 '13 at 14:13
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@YoubarajSharma: but the other question does not explain the difference between DECLARE and SET. It is just about the `DECLARE` syntax (rtfm-questions are off-topic on SO anyway). – Tim Schmelter Nov 19 '13 at 14:13
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@YoubarajSharma Actually that's the thing brought me here. I also read the manual pages that were linked. – C H Nov 19 '13 at 14:15
2 Answers
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DECLARE does not initialize the variable. When you declare it you declare the variable name, the type, and a default value, which could be an expression.
SET is for initializing the variable you declared previously, and you cannot SET the variable until you DECLARE it.
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Thank you! So you have to use both when creating a variable with a value unless you use "DEFAULT". Understood. – C H Nov 19 '13 at 14:22
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`you cannot SET the variable until you DECLARE it` not sure about version then, but we can't use `DECLARE` outside a stored procedure to declare a variable. We directly use `SET @newVar := 213` to declare as well as initialize – mr.loop Jan 05 '23 at 08:10
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DECLARE defines the variable type and SET initializes the variable.
DECLARE @Var1 INT;
DECLARE @Var2 INT;
SET @Var1 = 1;
SET @Var2 = 2;
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