Convert PostgreSQL backup to SQLite3

Working from a PostgreSQL backup

A PostgreSQL backup is not one thing. pg_dump can write plain SQL, a compressed custom-format archive or a tar archive, and all three routinely end up carrying the same .dump or .backup extension.

• →The first five bytes decide: PGDMP means an archive, which is unpacked with pg_restore, and anything else is treated as plain SQL. The extension is never trusted for this.
• →pg_restore is run with --file=- to print SQL to a pipe, so your backup is converted without ever being restored into a live PostgreSQL server: nothing connects to a database and nothing is created.
• →The directory format, pg_dump -Fd, is a folder rather than a file and cannot be uploaded. Re-dump it as -Fc or as plain SQL.

The .sqlite3 name and what carries over

The 3 in sqlite3 is the file format version and the name of the command-line tool, not a property of your conversion. One database file arrives, and the two things worth knowing about it are what it is called and what it leaves behind.

• →The file inside the zip is always database.sqlite, whichever spelling brought you to this page. Rename it to database.sqlite3, or to whatever a framework expects, once you have it - the header is what identifies it, never the extension.
• →An auto-increment column arrives holding all of its values and nothing that assigns new ones. No AUTOINCREMENT keyword is written, and the column is declared BIGINT rather than exactly INTEGER, so it is not an alias for the rowid either: rows you insert later have to supply their own key.
• →Only the rows are transactional. The very first CREATE TABLE runs in autocommit, and everything after it - that table's rows, and every later table - sits in one transaction that commits after the last row. A conversion that fails partway therefore leaves a file holding an empty shell of the first table and nothing else. You never receive that file: the zip is only assembled once the writer has returned.

Reading PostgreSQL backup

• →Reads pg_dump custom-format archives (.backup, .dump) — pgAdmin's default backup option — as well as plain SQL dumps.
• →Data written as COPY blocks is read, not just INSERT statements. COPY is pg_dump's default, so a reader that only understands INSERT returns your tables with none of their rows.
• →Primary keys declared by a later ALTER TABLE, which is how pg_dump writes them, are preserved.

Writing SQLite3

• →Columns get real declared types rather than everything being TEXT.
• →Primary keys and NOT NULL constraints are preserved.
• →A money column is declared NUMERIC(10,2), but that declaration does not stop SQLite’s own numeric affinity from converting the inserted value into a float once it lands, so 19.99 can come back with a rounding tail. Pick the DuckDB target instead when the exact decimal has to survive.

Convert PostgreSQL backup to something else

• MySQL
• PostgreSQL
• Oracle
• SQL Server
• DuckDB
• CSV
• Excel

Convert something else to SQLite3

• CSV
• Excel
• SQL dump
• DBF
• JSON
• XML
• Parquet
• DuckDB
• MS Access