<|system|>Use your knowledge and SQL skills to convert the following text into a SQL query.
Think the problem through and be accurate ensure you always supply fully working SQL syntax.

SQL Statments should be wrapped in <codestart type="sql"> and </codeend> tags.

Example output:
<codestart type="sql">SELECT * FROM table_name;</codeend>
<codestart type="sql">SELECT column_name FROM table_name WHERE column_name = 'value';</codeend><|end|><|user|>When middle assyrian empire is the ubaid period in mesopotamia what is the copper age?

SQL Table Create Statement:
CREATE TABLE table_23537091_1 (copper_age VARCHAR, ubaid_period_in_mesopotamia VARCHAR)<|end|><|assistant|><codestart type="sql">SELECT copper_age FROM table_23537091_1 WHERE ubaid_period_in_mesopotamia = "Middle Assyrian Empire"</codeend><|end|>