The Optimizer?

Hi all. This a very curious situation: take a table table_a ( column_1 char(3) not null, column_2 char(2) not null, column_3 smallint not null, column_4 integer, ... colum_n smallint, primary key (column_1,column_2,column_3)) Put into this table 5,500,000 records (or more ;-DDDD) execute the next sql statment: select * from table_a where column_2 = "xx" and column_2 = "yy" ***** This select is wrong because a column only could have a value in a record. Time expended to say "No records found" was 30 minutes with a lot of reads. Now replace the column_2 by column_1 in the where clausule (where column_1 = "xxx" and column_1 = "yyy") The time expended with this select = 0.00000001 miliseconds and 3 reads to say "No records found". Why the optimizer don't optimize the first select? Why the optimizer optimize the second select (because column_1 it's the first item of a index?) ? Work environment: SUN SparcServer 1000e with Solaris 2.4 and 4 Sparc-cpu and 256mb of RAM. INFORMIX: IDS v 7.27.UC7 Be patient XDD. --------------------------------------- Isidre PONS ROCA BASE - Gesti' d'Ingressos Locals (Diputacio de Tarragona) Servei de Sistemes de Informacio Av President Lluis Companys 12-C 43005 - Tarragona SPAIN Tel # +34 977 236731 Fax # +34 977 227302 http://www.altanet.org ipons@dtgna.altanet.org ---------------------------------------