SQL Tutorial 7: CONCAT function, ORDER BY, NULL value смотреть онлайн

How do you concatenate or combine columns and place it on a derived column? How do you check if a column contains NULL value? How do your arrange rows or records in descending or ascending order?

The video presents sample problems with solution as you work with a SELECT statement.

CONCAT () function combines data among columns. It is not limited with two columns but may work with multiple columns as you combine it with another CONCAT function. Use two double-pipe symbols (||) instead if you opt not to use CONCAT function.
Not all columns are filled up or has values on it in a given table. When a column contains no data even a single space, it has a NULL value. In using DB2 command line, a NULL column is represented by a single dash.

When generating a SELECT statement output it has no general sorting order on its result. To specify the correct sorting order, use ORDER BY clause after FROM. Ascending is the default order when sorting a particular column. If you want to sort in descending order, use DESC. Sort order is not limited with one column. You may combine with multiple columns by specifying which column to sort first followed by the next column order to sort.

CONCAT, ORDER BY, and NULL are universal in all dbms SQL products. It is the same if you use MS SQL Server, MySQl, Informix, Oracle, and DB2.

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