First, check whether the data in the amount column meets the decimal specification, and use cast (amount as? decimal( 10，4))& gt； 500 or

Convert (decimal (10,4), amount) > 500.

Note: The length and number of decimal places are set according to your own needs.

Convert string numbers into numbers in sql:

Method 1: choose CAST(' 123' as the signature? Integer);

Method 2: select convert (' 123', signed);

Method 3: Select'123'+0;

Extended data:

If you can convert a character type to a number type, you can convert a number to a character. For the data type of exact value, the converted string is the value we store. For example:

Declare @i int

set @i= 123456789

print ' test:'+convert(varchar(20)，@i)

The output is: test: 123456789.

However, it is not so simple for approximate numeric data types.

Declare @i float

set @i= 123456789

print ' test:'+convert(varchar(20)，@i)

Output result: test: 1.23457e+008.