Why does using an Underscore character in a LIKE filter give me all the results?

Question

I wrote the below SQL query with a LIKE condition:

SELECT * FROM Manager
WHERE managerid LIKE \'_%\'
AND managername LIKE \'%_%\'

Answer 1

The underscore is the wildcard in a LIKE query for one arbitrary character.

Hence LIKE %_% means "give me all records with at least one arbitrary character in this column".

You have to escape the wildcard character, in sql-server with [] around:

SELECT m.* 
FROM Manager m 
WHERE m.managerid    LIKE  '[_]%'
AND   m.managername  LIKE '%[_]%'

See: LIKE (Transact-SQL)

Demo