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Interesting properties of CROSS JOIN - SQL
Compare these with the "interesting properties of JOIN", CROSS JOIN is associative but not commutative. Unlike JOIN and NATURAL JOIN, CROSS JOIN is not idempotent. Let t be any table and let n be its cardinality. Then t CROSS JOIN t has twice as many columns as t and n2 rows. Also unlike JOIN, CROSS JOIN has no identity value. If t is a table, there is no table t0 such that t CROSS JOIN t0 = t. That's because t0 would be required to have no columns and exactly one row, but SQL doesn't recognize the existence of tables with no columns.
Effects of NULL for Table Expression Here's an important distinction between expressions denoting tables and expressions denoting multisets of rows: a table expression cannot
Example of WHEN or THEN Constraints A concrete example showing how SQL supports WHEN/THEN constraints CREATE TABLE SAL_HISTORY (EmpNo CHAR (6), Salary INTEGER NOT NULL,
Mutual Recursion The Subprograms are mutually recursive if they directly or indirectly call each other. In the illustration below, the Boolean functions odd & even, that dete
Package STANDARD The package named STANDARD defines the PL/SQL atmosphere. The package specification globally declares the exceptions, types, and subprograms that are available
Table Comparison - SQL The following definitions for relation comparisons: Let r1 and r2 be relations having the same heading. Then: r1 ⊆ r2 is true if every tuple of r1
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Declaring and Initializing Objects: An object type is once defined and installed in the schema; you can use it to declare the objects in any PL/SQL, subprogram, block or packa
LIKE Operator You use the LIKE operator to compare the character value to a pattern. The Case is significant. LIKE returns the Boolean value TRUE when the character patterns mat
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