You don't have where clause in your update, so all rows of t1 are updated.
And as you have no row in t2 with id=1, the select return a null value.

Le 6 mars 2012 02:19, TXVanguard <> a écrit :

When I run the following SQL statements in JavaDB:


drop table t1;
drop table t2;

create table t1 ( TXT1 varchar(6), ID integer );

create table t2 ( ID integer, TXT2 varchar(12));

insert into t1 (TXT1,id) values ('ONE',1);
insert into t1 (TXT1,id) values ('TWO',2);

insert into t2 (id,TXT2) values (2,'TWO');
insert into t2 (id,TXT2) values (3,'THREE');

UPDATE t1 SET TXT1 = (select (TXT2) FROM t2 WHERE (t2.ID = t1.ID));


then, table t1 has the following values:

           VAL1      ID
ROW 1: <NULL>      1
ROW 2: 'TWO'         2

Why is the value of column VAL1 in the first row set to <NULL> by the update
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