SELECT Statement The same precedence interpretation also applies to statements that mix the comma operator with  INNER JOIN ,  CROSS JOIN ,  LEFT JOIN , and  RIGHT JOIN , all of which have higher precedence than the comma operator. SELECT * FROM t1 JOIN t2 JOIN t3 ON (t1.i1 = t3.i3); •Avoid the use of the comma operator and use  JOIN  instead: •A MySQL extension compared to the SQL:2003 standard is that MySQL permits you to qualify the common (coalesced) columns of  NATURAL  or  USING  joins, whereas the standard disallows that. 13.2.10.3 UNION Clause SELECT ... UNION [ALL | DISTINCT] SELECT ... [UNION [ALL | DISTINCT] SELECT ...] UNION  combines the result from multiple  SELECT  statements into a single result set. Example: mysql>  SELECT 1, 2; +---+---+ | 1 | 2 | +---+---+ | 1 | 2 | +---+---+ mysql>  SELECT ’a’, ’b’; +---+---+ | a | b | +---+---+ | a | b | +---+---+ mysql>  SELECT 1, 2 UNION SELECT ’a’, ’b’; +---+---+ | 1 | 2 | +---+---+ | 1 | 2 | | a | b | +---+---+ •Result Set Column Names and Data Types •UNION DISTINCT and UNION ALL •TABLE in Unions •ORDER BY and LIMIT in Unions •UNION Restrictions •UNION Handing in MySQL 8.0 Compared to MySQL 5.7 Result Set Column Names and Data Types The column names for a  UNION  result set are taken from the column names of the first  SELECT  statement. Selected columns listed in corresponding positions of each  SELECT  statement should have the same data type. For example, the first column selected by the first statement should have the same type as the first column selected by the other statements. If the data types of corresponding  SELECT  columns do not match, the types and lengths of the columns in the  UNION  result take into account the values retrieved by all the  SELECT  statements. For example, consider the following, where the column length is not constrained to the length of the value from the first  SELECT : 2677