SHOW SOURCES FOR

The SHOW SOURCES FOR statement lists the tables whose data is in a table right now — one row per source, most recently read first. It answers "what is this table made of?"

It is the short companion to SHOW LINEAGE FOR. Lineage lists every commit's receipt, so it tells you what each version was built from over the table's whole history. Sources is those receipts rolled up for the current contents, and kept on the table itself, so it answers from a single read. No history is loaded and no data files are read.

Syntax

sql

SHOW SOURCES FOR <table_name>;

Bare SHOW SOURCES is not supported, and neither is SHOW SOURCES FROM. A source list belongs to one table, so name it with the FOR form.

Parameters

<table_name> — fully qualified as <workspace>.<collection>.<table_name>.

Result Columns

Column	Description
`source_dataset`	The fully qualified name of a table whose data is in this table's current contents
`position`	`0` for the most recently read source, counting up. Stated explicitly so the order survives a client that re-sorts by name
`complete`	Whether the list is known to hold every source. See Completeness

complete is repeated on every row, not reported once, so the result has one shape.

How the List Is Kept

The list is maintained by the commits themselves, from each commit's receipt (see SHOW LINEAGE FOR). What a commit does to it depends on what the commit did to the data:

Commit	Effect on the list
An append, merge or update	The sources it read are added at the front; names already there move to the front
An overwrite, or a truncate that adds files	The list is replaced by the sources the commit read, because none of the old content remains
A truncate	The list is cleared
A delete that leaves no rows	The list is cleared
Compaction, statistics refresh	Unchanged. The content is the same content
A rollback	Recomputed from the receipts along the chain the table now rests on

A table is never in its own source list, even when the statement that wrote it read it, as a MERGE does when it matches against its target.

The list holds the current content's sources, not everything the table has ever read. A table that was rebuilt last night from a different source no longer lists the old one, though its lineage still does.

Completeness

The list can be missing a name in two cases, and complete is false when either has happened:

The cap. The list holds at most 64 names. If more than that contributed, the oldest are dropped.
A commit with no receipt. A commit made before receipts existed, or through an engine older than the catalog, contributes nothing the list could record. Any table with history from before receipts is incomplete by definition.

complete returns to true after the next overwrite or truncate, because both start the list afresh.

complete can also be null: the catalog did not say, which is what a table from before the field existed reports. That is a different answer from false.

An empty list is one row, with source_dataset and position both null, so that complete can still be read:

`source_dataset`	`complete`	Means
`null`	`true`	Built from nothing: literals, uploads, `INSERT ... VALUES`
`null`	`false`	Built from nothing that was recorded

Examples

What Is This Table Made Of?

sql

SHOW SOURCES FOR my_workspace.reports.monthly_summary;

Which Version of Each Source?

SHOW SOURCES FOR names the tables but not the versions. For the snapshot of each that a commit read, use SHOW LINEAGE FOR:

sql

SHOW LINEAGE FOR my_workspace.reports.monthly_summary;

Notes

Requires read access to the table you name, the same as a SELECT against it. Every source is named, including one in a workspace you have no grant on. A name in a source list is a citation, not access, and reading the source still needs a grant of its own.
Catalog-backed tables only. A table on a store that keeps no commit log reports that it has no source list, rather than an empty one.
Declared is not the same as read. A materialized view's declared sources are what it is defined to read. This list is what its refreshes have read.
Always returns the whole list. SHOW statements have no WHERE clause or column list, and the result is not a subquery source, so filter the rows client-side.
Free to run. One document is read. No history is loaded and no data files are read.