For example, this is a an inner self-join: SELECT * FROM A A1 JOIN A A2 ON LEN(A1.X) < LEN(A2. A self-join can be any of the join types discussed above. This simply denotes a table joining with itself. SELECT * FROM A CROSS JOIN B Ĭross join is equivalent to an inner join with join condition which always matches, so the following query would have returned the same result: SELECT * FROM A JOIN B ON 1 = 1 right anti semi join - we achieve the effect simply by switching the table positions within SQL text.Ī Cartesian product of all left with all right rows. SELECT * FROM B WHERE Y NOT IN (SELECT X FROM A) Īs you can see, there is no dedicated NOT IN syntax for left vs. Includes right rows that do not match left rows. WARNING: Be careful if you happen to be using NOT IN on a NULL-able column! More details here. SELECT * FROM A WHERE X NOT IN (SELECT Y FROM B) Cross joins are queries where each row from the first table is joined to every row in the second table (. Includes left rows that do not match right rows. When a CROSS JOIN is required, pre-aggregate your data. right semi join - we achieve the effect simply by switching the table positions within SQL text. SELECT * FROM B WHERE Y IN (SELECT X FROM A) Īs you can see, there is no dedicated IN syntax for left vs. Includes right rows that match left rows. SELECT * FROM A WHERE X IN (SELECT Y FROM B) Lookup joins are used when there is a large imbalance in size between the two tables, as it only reads the smaller table and then looks up matches in the larger. Includes left rows that match right rows. Combines left and right rows that match, and includes non-matching right rows. Combines left and right rows that match, and includes non-matching left rows. The examples below use the following test data: CREATE TABLE A ( We can use various join types to include or exclude matching or non-matching rows from either side, and correctly name the join by picking the corresponding terms from the diagram above. Let's say we have two tables (A and B) and some of their rows match (relative to the given JOIN condition, whatever it may be in the particular case):
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