Proc Sql Left Join 2 Tables

masuzi December 11, 2018 Uncategorized Leave a comment 2 Views

When it comes to working with databases, the left join is one of the most important techniques to know. A left join lets you combine two tables with each other by matching up rows from both tables and copying over data. This join type is especially useful when you want to make sure that all the data from one table is included in the result, even if there are no matching rows in the other table. The best way to understand how this works is to look at an example.

Let's say we have two tables - one with customer orders and another with customer addresses. We can use a proc sql left join to combine these two tables together. This means that for each order, we will get the customer's address - even if the customer has not yet provided their address. The resulting table will contain all the orders from the first table, along with any matching address information from the second.

Using proc sql syntax, the left join looks like this:

proc sql;
select *
from orders
left join addresses on orders.customerid = addresses.customerid;
quit;

This statement will select all columns from both tables and match up the customerid columns. Any orders where the customerid doesn't match up with an address will still be included, but the address fields will be blank.

To understand how this works, let's take a look at a simplified example. Imagine we have two tables, called orders and addresses. The orders table contains two columns: customerid and orderid. The addresses table has three columns: customerid, street, and city.

We can use a proc sql left join to combine these two tables and get a result that includes all the orders, along with the customer's address if they have provided one. To do this, we need to specify which columns we want to match up. In this case, we'll match up the customerid column from both tables. The resulting table will have four columns: customerid, orderid, street, and city.

The proc sql syntax for this left join looks like this:

proc sql;
select *
from orders
left join addresses on orders.customerid = addresses.customerid;
quit;

This statement will select all columns from both tables and match up the customerid columns. Any orders where the customerid doesn't match up with an address will still be included, but the address fields will be blank.

This example shows how powerful proc sql left joins can be. By combining two tables, you can quickly build up a result set that includes data from both tables. Plus, you don't need to worry about missing data - the left join will make sure that all the records from the first table are included, even if there are no matching rows in the second.

The proc sql syntax is quite simple, but mastering the technique takes practice. To help you get started, here are a few tips for using proc sql left joins:

- Make sure you specify the correct columns to match up - otherwise, you won't get the results you expect.
- If you're joining multiple tables, make sure you use the correct syntax for each join.
- Remember that the left join will include all records from the first table, even if there are no matches in the second.
- Keep an eye out for blank address fields in your results - this could indicate that the customer has not yet provided their address.

By using proc sql left joins, you can quickly and easily combine two tables. With a bit of practice, you'll soon be a pro at writing efficient left join statements.