Discovering BigQuery SQL
BigQuery supports two different SQL dialects: standard SQL and legacy SQL. In this book, we'll use Standard SQL, but it could be useful to know what Legacy SQL is and how to enable it if you want to test queries coming from legacy applications.
As we have already mentioned, BigQuery was developed as an internal product within Google and was initially realized to process log records. The query engine Dremel was able to support a limited set of SQL operations that are now defined as Legacy SQL.
In the following screenshot, you can see how to change the SQL dialect:
By default, the BigQuery UI is configured to use Standard SQL, but you are allowed to change the SQL dialect by using the specific option located in the Query Settings of the BigQuery web interface, or by prefacing your queries with the #legacySQL
keyword in the first line of your SQL...