To run statements in Oracle from the command line, a semicolon must be added. : SQL PLUS Editor « SQL PLUS Session Environment « Oracle PL/SQL Tutorial

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2. SQL PLUS Session Environment
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From the editor, a slash (/) is added to execute the statement and no semicolon is used.

SQL> SELECT SUBSTR('My address is 123 Fourth St.',1,12)FROM dual
  2  /

SUBSTR('MYAD
------------
My address i

SQL>