Question

I have two tables containing peoples data, first name, last name etc.

The first table contains the data I want to select if it matches the stuff from the second table. The problem is the first table might have only an initial for the first name.

I have tried variations of the following query but I am missing something obviously. I don’t mind if “J Bloggs” and “Joe Bloggs” from table 1 both match “Joe Bloggs” from table 2 that’s fine.

SELECT t1.* ,  LEFT(t2.FIRST_NAME, 1) AS firstChar 
FROM t1, t2
WHERE t1.surname = t2.LAST_NAME
AND t1.firstname  = t2.FIRST_NAME
OR t1.firstname  = t2.firstChar
GROUP BY t1.surname

Answer 1

You need to put () around your second WHERE condition as in:

SELECT t1.* ,  LEFT(t2.FIRST_NAME, 1) AS firstChar 
FROM t1, t2
WHERE 
  t1.surname = t2.LAST_NAME
  AND (t1.firstname  = t2.FIRST_NAME OR t1.firstname  = LEFT(t2.FIRST_NAME, 1)
ORDER BY t1.surname

However, the implicit join syntax is discouraged and deprecated. Instead, use

SELECT t1.* ,  LEFT(t2.FIRST_NAME, 1) AS firstChar 
FROM 
  t1 JOIN t2 
    ON t1.surname = t2.LAST_NAME
      AND (t1.firstname  = t2.FIRST_NAME OR t1.firstname  = LEFT(t2.FIRST_NAME, 1)
ORDER BY t1.surname

Since your condition is that the last name must match, and the first name must either match fully or match the first character, the first name conditions have to be grouped inside ().

I have also replaced your GROUP BY with ORDER BY, since you are not performing any group aggregate functions (SUM(), COUNT(), AVG()). MySQL doesn’t permit aliases in the WHERE clause, so I have replaced t2.firstChar with LEFT(t2.firstChar, 1) as well.

Finally, you may find a need to convert the case of all the names with UPPER() or LOWER() on both sides of the join to be sure it matches where casing may be inconsistent.