Question

Let say that I have table TableA(ColumnCode, ColumnA2, ColumnA3, ColumnA4, ColumnA5).

Note: ColumnCode(PrimaryKey)is not autoincrement. What I want to prevent is following scenario:

INSERT INTO TableA VALUES(1111, 'val1a', 'val2a', 'val3a', 'val4a', 'val5a')

Next insert is with the same values but different ColumnCode:

INSERT INTO TableA VALUES(1234, 'val1a', 'val2a', 'val3a', 'val4a', 'val5a')

The thing is that I want to prevent inserts like this, where I might have these situations of inserting same values just for another ColumnCode.

Any idea?

Note2: Next insert is not a problem because I’m not inserting ALL the same column values!!!

INSERT INTO TableA VALUES(1456, 'val1a', 'val2a', 'val3a', 'val32a', 'val654a')

As shown, set(ColumnA2, ColumnA3, ColumnA4, ColumnA5) of values is not a duplicate. ColumnA4 and ColumnA5 values are different. So, for me, a duplicate is only when all four of ColumnA values are in table under any ColumnCode.

Hope I cleared my question a bit?

Answer 1

You might want to take a look at using SQL UNIQUE Constraint

The UNIQUE constraint uniquely identifies each record in a database
table.

The UNIQUE and PRIMARY KEY constraints both provide a guarantee for
uniqueness for a column or set of columns.

A PRIMARY KEY constraint automatically has a UNIQUE constraint defined
on it.

Note that you can have many UNIQUE constraints per table, but only one
PRIMARY KEY constraint per table.

Have a look at the following example ….

SQL Fiddle DEMO

CREATE TABLE TABLE1(
  col1 varchar(50) PRIMARY KEY,
  col2 varchar(50),
  col3 varchar(50),
  col4 varchar(50),
  CONSTRAINT uc UNIQUE (col2,col3,col4)
 );

this should work:

INSERT INTO TABLE1 VALUES('1','1','1','1');
INSERT INTO TABLE1 VALUES('2','1','1','2');

this should fail:

INSERT INTO TABLE1 VALUES('1','1','1','1');
INSERT INTO TABLE1 VALUES('2','1','1','1');