Select Command in SQL Server
The SQL Server Select statement is the first statement used when returning data. It is the most used and most important statement in the T-SQL language. The Select statement has many different clauses. We will step through each clause further in the tutorial, however now, we will look at Select itself.
As we can see from our results, the code returns one row, one column. The data of the column returned is the value: ‘Jems’. The column’s name is ‘FirstName’.
The ‘AS’ allows you to specify a column alias. This alias could be anything, in this case we made it ‘FirstName’. We can also Select multiple columns of data by separating the columns using a comma:
These examples so far, have only used the Select statement by itself. Now we will explore using Select in addition with the ‘From’ clause. The From Clause allows a source to be specified for the Select Statement. For the purposes of this example, the source is always a table. Let’s look at an example.
The above query is pronounced: Select star from Person dot Person. The star (*) or asterisks is notation for saying “all columns”. Basically, the query is saying give me all columns from the Person table contained within the Person Schema. The person schema is basically a class, or a way to better organize tables. This example will return every column for every row of the ‘MSreplication_options’ table. We could also specify specific columns in order to limit the results:
This query would return all rows for the three columns listed. Now suppose we did not want to return all the columns listed. Instead, we only want to return MSreplication_options with the optname of ‘merge’. This is where the ‘From’ clause comes in.
The Where clause is where the power of SQL begins to get introduced. We can also provide more specifics regarding the rows we want to return by adding additional criteria in the where clause. We do this by specifying the AND statement.
OR operator use with WHERE clause.