Question 1

How to translate SQL from Spark to BigQuery using SQLGlot?

Accepted Answer

Use the transpile function with read='spark' and write='bigquery', e.g., sqlglot.transpile('SELECT * FROM table', read='spark', write='bigquery'). Always specify both dialects to avoid defaulting to the SQLGlot dialect, which might not output correct SQL.

Question 2

SQLGlot vs sqlparse: which is better for SQL parsing in Python?

Accepted Answer

SQLGlot is more comprehensive for transpilation, optimization, and AST manipulation across multiple dialects, while sqlparse is lighter and focused solely on parsing and formatting. Choose SQLGlot for cross-database tasks or programmatic analysis, and sqlparse for simple formatting without dialect translation.

Question 3

Can SQLGlot handle nested subqueries in optimization?

Accepted Answer

Yes, SQLGlot's optimizer can rewrite nested subqueries as part of its canonicalization techniques, but it requires schema information to be effective. The README shows examples with complex queries, but note that optimization is not enabled by default due to performance costs.

Question 4

How to install SQLGlot with C extensions for better performance?

Accepted Answer

Install via pip with 'sqlglot[c]', e.g., pip3 install 'sqlglot[c]'. This uses prebuilt wheels if available or compiles from source, providing faster parsing as demonstrated in benchmarks where C extensions reduce parsing time by up to 75%.

Question 5

What databases does SQLGlot support officially?

Accepted Answer

Official dialects include DuckDB, Spark, Snowflake, BigQuery, MySQL, Postgres, and Trino, among others. Community dialects exist but may have lower priority for bug fixes; check the supported dialects table in the README for details.

Question 6

How to create a custom dialect plugin in SQLGlot?

Accepted Answer

Subclass the Dialect class and define tokenizer and generator components, then register it via entry points in setup.py. The README provides an example with custom keywords and type mappings, allowing external packages to extend support.

SQLGlot

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