Returns a count of the number of non-NULL values of expr in the rows retrieved by a SELECT statement. The result is a BIGINT value.
If there are no matching rows, COUNT() returns 0.
This function executes as a window function if over_clause is present. over_clause is as described in Section 12.21.2, “Window Function Concepts and Syntax”.
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mysql>SELECT student.student_name,COUNT(*) FROM student,course WHERE student.student_id=course.student_id GROUPBY student_name;
COUNT(*) is somewhat different in that it returns a count of the number of rows retrieved, whether or not they contain NULL values.
# =================================================================== # COMMON SPRING BOOT PROPERTIES # # This sample file is provided as a guideline. Do NOT copy it in its # entirety to your own application. ^^^ # ===================================================================