Using CASE to avoid '':
CREATE TABLE test (number TEXT);
INSERT INTO test VALUES('123');
INSERT INTO test VALUES('a123b');
INSERT INTO test VALUES('');
teste=> SELECT CASE number WHEN '' THEN NULL ELSE
to_number(number,'999999999999990') END AS
number FROM test;;
number
--------
123
123
(3 lines)
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TIP 9: In versions below 8.0, the planner will ignore your desire to
choose an index scan if your joining column's datatypes do not
match
