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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.
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,
Data Types in SQL - Character CHARACTER or, synonymously, CHAR, for character strings. When this type is to be the declared type of something (e.g., a column), the permissible
Effects of NULL in Aggregate Operator - SQL Let aggop(x) be an invocation of some aggregate operator aggop in SQL, where x is an expression (usually an open expression) to be
Example of Check Constraints Example: Workaround for when subqueries not permitted in CHECK constraints CREATE FUNCTION NO_MORE_THAN_20000_ENROLMENTS ( ) RETURNS BOOLEAN
Using NOT NULL Besides assigning an initial value, the declarations can impose the NOT NULL constraint, as the example below shows: acct_id INTEGER(4) NOT NULL := 9999; You ca
Example of NOT EXISTS in SQL Example: Use of NOT EXISTS CREATE ASSERTION Must_be_enrolled_to_take_exam_alternative1 CHECK ( NOT EXISTS (SELECT StudentId, CourseId
Assigning and Comparing Collections One collection can be assigned to other by an SELECT, INSERT, UPDATE, or FETCH statement, an assignment statement, or by a subprogram call. A
Mixed Notation The fourth procedure call shows that you can mix the positional and named notation. In this situation, the first parameter uses the positional notation, & the s
Table Literals - SQL One might expect SQL to support table literals in the manner illustrated in Example 2.2, but in fact that is not a legal SQL expression. Example: Not a
Challenge 1 You are required to do the project and write a test plan for it. Demo 4 is a check writer program for employees. In it, the user enters all information about the
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