Coding Cheatsheets - Learn to Code

The UNION set operator is used for combining data from two tables which have columns with the same datatype.When a UNION is performed the data from both tables will be collected in a single column having the same datatype. Rules: The number of columns appears in the corresponding SELECT statements must be equal. The columns appear in  the corresponding positions of each SELECT statement must have the same data type or at least convertible data type. You cannot use the union operator on text and image columns. Notes: Union -- returns with no duplicate rows Union all -- retruns with duplicate rows (No. of rows returned = No. of rows in Query1 + No. of rows in Query 2) Example: Suppose you want to combine data from the  student and teacher tables into a single result set, you can UNION operator as the following query: SELECT studentNumber id, contactLastname name FROM student UNION SELECT teacherNumber id,firstname name FROM teacher Here is the output...