CREATE TABLE

New in v0.5.0:

CREATE TABLE creates an in-memory table.

Conceptual framework

Tables in Materialize are similar to tables in standard relational databases: they consist of rows and columns where the columns are fixed when the table is created but rows can be added to at will via INSERT statements.

You can seamlessly join tables with other tables, views, and sources in the system.

WARNING! At the moment, tables serve a niche use case. They lack many features that are standard in relational databases. In most situations you should use sources instead.

When to use a table

A table can be more convenient than a source, but only if all of the following statements are true:

Your dataset is either static or append only.
You do not need the dataset to survive reboots of Materialize.
Your dataset is several times smaller than the available memory on your machine. See the memory usage section below for details.

If any of those statements do not describe your situation, we recommend that you use a source instead.

Syntax

`col_option`

Field	Use
TEMP / TEMPORARY	Mark the table as temporary.
table_name	A name for the table.
col_name	The name of the column to be created in the table.
col_type	The data type of the column indicated by col_name.
NOT NULL	Do not allow the column to contain NULL values. Columns without this constraint can contain NULL values.
default_expr	A default value to use for the column in an `INSERT` statement if an explicit value is not provided. If not specified, `NULL` is assumed.

Details

Restrictions

WARNING! Tables do not persist any data that is inserted. This means that restarting a Materialize instance will lose any data that was previously stored in a table.

Additionally, tables do not currently support:

Primary keys
Unique constraints
Check constraints
Insert statements that refer to data in other relations, e.g.:
```
INSERT INTO t1 SELECT * FROM t2
```
UPDATE ... and DELETE statements

Temporary tables

The TEMP/TEMPORARY keyword creates a temporary table. Temporary tables are automatically dropped at the end of the SQL session and are not visible to other connections. They are always created in the special mz_temp schema.

Temporary tables may depend upon other temporary database objects, but non-temporary tables may not depend on temporary objects.

Memory usage

Every table is backed by an index that materializes all of the data in the table. Unlike sources, tables cannot be “unmaterialized”. Therefore you must ensure that the data you store in tables fits in the amount of memory you have available on your system. Remember that any additional indexes or derived materialized views will count against your memory budget.

If your dataset is too large to fit in memory, consider using an unmaterialized source instead. This lets you defer materialization to views derived from this source, which can aggregate or filter the data down to a manageable size.

Examples

Creating a table

You can create a table t with the following statement:

CREATE TABLE t (a int, b text NOT NULL);

Once a table is created, you can inspect the table with various SHOW commands.

SHOW TABLES;
TABLES
------
t

SHOW COLUMNS IN t;
name       nullable  type
-------------------------
a          true      int4
b          false     text

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