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Explicitly specifying the join condition - SQL
SELECT *
FROM IS_CALLED JOIN IS_ENROLLED_ON
ON ( IS_CALLED.StudentId = IS_ENROLLED_ON.StudentId )
Now, the key word JOIN in all of the foregoing examples can be harmlessly preceded by the word INNER. SQL also supports what are called "outer joins". The outer join of t1 and t2 contains all the rows of the inner join and possibly some more if either operand has rows which fail to participate in the inner join. Such a row might participate in the outer join, accompanied by NULL for each column of the other operand. The key words LEFT, RIGHT, and FULL, each optionally followed by OUTER, are used to specify whether unmatched rows of the first (left) operand, the second (right) operand, or both operands, respectively, are to appear in the result. Example shows an SQL outer join. A single row for student S5 appears in the result, with NULL in place of a value for CourseId.
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Example of ADD CONSTRAINT in SQL Example: Alternative formulation for MAX_ENROLMENTS ALTER TABLE IS_ENROLLED_ON ADD CONSTRAINT MAX_ENROLMENTS CHECK ((SELECT COUNT (*)
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