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This article is about what "select 1 from table" means in sql. The editor thinks it is very practical, so share it with you as a reference and follow the editor to have a look.

What does "select 1 from table" mean?

Select 1 from table and Select * from table are more or less the same in usage. For more information, please see the following:

1. Select 1 from mytable; and select anycol (any row in the destination table set) from mytable; and select * from mytable are no different in function. They all check whether there is a record, which is generally used as a condition.

1 in select 1 from is a constant, which is the value of all rows found, but in terms of efficiency, 1 > anycol > *, because there is no need to look up the dictionary table.

2. To view the number of records, you can use select sum (1) from mytable; to be equivalent to select sum (*) from mytable

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