There are two types of temporary tables:
Local temporary tables
The names of these tables begin with one number sign (#). These tables are visible only to the connection that created them.
Global temporary tables
The names of these tables begin with two number signs (##). These tables are visible to all connections. If the tables are not dropped explicitly before the connection that created them disconnects, they are dropped as soon as all other tasks stop referencing them. No new tasks can reference a global temporary table after the connection that created it disconnects. The association between a task and a table is always dropped when the current statement completes executing; therefore, global temporary tables are usually dropped soon after the connection that created them disconnects.
Darrell Norton, MVP
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