REPLACE ( (select FName AS 'data ()' from NameList for xml path ('')), ' ', ', ') Share. Instead of adding a comma, use of the AS 'data ()' will concatenate the rows with spaces, which later can be replaced with commas as the syntax written below. Therefore, they’re used in the payment table as a foreign key. For the extra comma we can use the replace function of SQL Server. Note that the student_id and course_code columns form a primary key in the enrollment table. In the next condition, we get the course_code column from the enrollment table and course_code from the payment table. In the first part, we use the student_id column from the enrollment table and student_id from the payment table. P.course_code=e.course_code AND p.student_id=e.student_id How can we join the tables with these compound keys?Įasy! We just need to use a JOIN clause with more than one condition by using the AND operator after the first condition. In the second table ( payment), we have columns that are a foreign compound key ( student_id and course_code). This is an aggregate (GROUP BY) function that returns a String value if the group contains at least one non-NULL value. In one joined table (in our example, enrollment), we have a primary key built from two columns ( student_id and course_code). The GROUPCONCAT () function in MySQL is used to concatenate data from multiple rows into one field. If you’d like to get data stored in tables joined by a compound key that’s a primary key in one table and a foreign key in another table, simply use a join condition on multiple columns. Let’s show each student’s name, course code, and payment status and amount. The payment table has data in the following columns: foreign key ( student_id and course_code, the primary keys of the enrollment table), status, and amount. The enrollment table has data in the following columns: primary key ( student_id and course_code), is_active, and start_date. Instead the ELT function one can use IF or CASE. Each query row can be filled by the appropriate data. Now we have three rows in our query for each row in the base table foo. The student table has data in the following columns: id (primary key), first_name, and last_name. We want to create 3 rows for each row of the foo table, so we create an auxiliary table containing three rows and (cross) join it to the foo table. Our database has three tables named student, enrollment, and payment. You want to join tables on multiple columns by using a primary compound key in one table and a foreign compound key in another.
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