Drop a foreign key constraint between columns of two tables without knowing the foreign key name in Informix?

问题

I'm using an Informix database. I have added some foreign keys to a table without giving them a name e.g.

ALTER TABLE myreport
  ADD CONSTRAINT FOREIGN KEY (rid) REFERENCES report(id),
  ADD CONSTRAINT FOREIGN KEY (uid) REFERENCES user(id);

Now I want to delete the foreign key between uid and id of user table.

I can get the name of the constraints on the table using the following:

SELECT constrname
  FROM sysconstraints
 WHERE tabid = (SELECT tabid FROM systables WHERE tabname = 'myreport');

which gives following output:

constrname  u169_201    
constrname  n169_202
constrname  n169_203
constrname  n169_204
constrname  n169_205
constrname  n169_206
constrname  n169_207
constrname  r169_276
constrname  r169_277

I don't know which constraint belongs to the foreign key between uid and id of user table.

回答1:

Try using the sysreferences catalog table. Something like this should give you the information you need:

SELECT
    c_a.constrname AS Constraint_name
    , t_a.tabname AS ForeignKey_table
    , i_a.idxname AS ForeignKey_index
    , t_b.tabname AS PrimaryKey_table
    , i_b.idxname AS PrimaryKey_index 
FROM
    sysreferences AS r
    INNER JOIN sysconstraints AS c_a
    ON 
        r.constrid = c_a.constrid
    INNER JOIN systables AS t_a
    ON 
        c_a.tabid = t_a.tabid
    INNER JOIN systables AS t_b
    ON 
        r.ptabid = t_b.tabid
    INNER JOIN sysindexes AS i_a
    ON
        c_a.idxname = i_a.idxname
    INNER JOIN sysconstraints AS c_b
    ON
        r.primary = c_b.constrid
    INNER JOIN sysindexes AS i_b
    ON
        c_b.idxname = i_b.idxname 
WHERE
    t_a.tabname = 'YOUR_TABLE_HERE';

回答2:

I tried following it worked:

CREATE PROCEDURE INFORMIX.REMOVE_FK()
    DEFINE tmpvr varchar(250);
    FOREACH cur1 FOR select  b.constrname into tmpvr
            from systables a, sysconstraints b, sysindexes c, syscolumns d
            WHERE a.tabname = 'myreport' AND (d.colname='uid' or d.colname='rid')
            AND b.tabid = a.tabid AND c.idxname = b.idxname AND d.tabid = a.tabid AND (
                d.colno = c.part1 or d.colno = c.part2 or d.colno = c.part3 or d.colno = c.part4 or
                d.colno = c.part5 or d.colno = c.part6 or d.colno = c.part7 or d.colno = c.part8 or
                d.colno = c.part9 or d.colno = c.part10 or d.colno = c.part11 or d.colno = c.part12 or
                d.colno = c.part13 or d.colno = c.part14 or d.colno = c.part15 or d.colno = c.part16
            )
    EXECUTE IMMEDIATE 'ALTER TABLE myreport DROP CONSTRAINT (' || tmpvr || ')';
    END FOREACH
END PROCEDURE;
EXECUTE PROCEDURE INFORMIX.REMOVE_FK();
DROP PROCEDURE INFORMIX.REMOVE_FK();

来源：https://stackoverflow.com/questions/46466980/drop-a-foreign-key-constraint-between-columns-of-two-tables-without-knowing-the

标签

mysql

informix