Generating Data
Explore the various methods to generate data in SQL for practice, simulations, or time series analysis. Understand how to use SELECT clauses, UNION ALL, the VALUES keyword, UNNEST function, and generate_series to create single and multiple rows of data efficiently.
Generating data is very handy. Sometimes, we need to generate data for practice. Sometimes, we want to run performance simulations and need a big table to work with. Other times we might need to generate a sequence such as a time dimension in a data warehouse, or an axis table to join to in an anomaly detection system.
There are many reasons to generate data in SQL, and in this chapter we’ll learn several ways to do that.
The SELECT clause
The most straightforward way to to generate data in SQL is using the SELECT clause:
This query will produce a single row with the id column and the name column. Notice that this query is not fetching from any table. In fact, in SQL, the only required clause is SELECT.
Generating just one row is useful, but what if we need to generate more than one row?
The UNION ALL command
To combine the results of multiple queries we can use UNION ALL:
We used UNION ALL to concatenate the ...