I taught myself, really do not understand ah, not the data in the table also shows? Is meaningless, and even affect the normal query?

CodePudding user response:

This has nothing to do with what tools you use, this is one of the SQL returns the constant writing;
Generally used in the program is less (typically used to define constants in program, less write death in SQL); Practice, used in the daily statistics and guide in the table will be a little more;

CodePudding user response:

This is not a sqlyog features, in mysql can retrieve them directly without any reference table, SELECT equivalent to SELECT 1 FROM DUAL, then put the FROM DUAL neglect,