Add Create And Execute SQL Statements With \gexec as a Postgres TIL

Author: jbranchaud

Diff for: README.md

@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
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+_1635 TILs and counting..._
 
 See some of the other learning resources I work on:
 - [Ruby Operator Lookup](https://www.visualmode.dev/ruby-operators)
@@ -820,6 +820,7 @@ If you've learned something here, support my efforts writing daily TILs by
 - [Create A Table From The Structure Of Another](postgres/create-a-table-from-the-structure-of-another.md)
 - [Create An Index Across Two Columns](postgres/create-an-index-across-two-columns.md)
 - [Create An Index Without Locking The Table](postgres/create-an-index-without-locking-the-table.md)
+- [Create And Execute SQL Statements With \gexec](postgres/create-and-execute-sql-statements-with-gexec.md)
 - [Create Database Uses Template1](postgres/create-database-uses-template1.md)
 - [Create hstore From Two Arrays](postgres/create-hstore-from-two-arrays.md)
 - [Create Table Adds A Data Type](postgres/create-table-adds-a-data-type.md)

Diff for: postgres/create-and-execute-sql-statements-with-gexec.md

@@ -0,0 +1,58 @@
+# Create And Execute SQL Statements With \gexec
+
+The [`\gexec`
+meta-command](https://www.postgresql.org/docs/current/app-psql.html#APP-PSQL-META-COMMAND-GEXEC)
+is a variation of the [`\g`
+meta-command](https://www.postgresql.org/docs/current/app-psql.html#APP-PSQL-META-COMMAND-G),
+both of which can be used in a `psql` session. Whereas the `\g` command sends
+the current query in the buffer to the PostgreSQL server for execution, the
+`\gexec` command first sends the query to the server for execution and then
+executes each row of the result as its own SQL statement.
+
+This is both a bit absurd and powerful. And a bit unnecessary considering all
+of the scripting capabilities with anything from bash to any language with a
+SQL client library.
+
+Nevertheless, let's take a look at a contrived example of how it works. Here,
+we have a SQL statement that does some string concatenation based off values in
+an array. This results in three separate `create schema` statements.
+
+```sql
+> select
+    'create schema if not exists schema_' || letter || ';'
+  from unnest(array['a', 'b', 'c']) as letter
+  \gexec
+
+CREATE SCHEMA
+CREATE SCHEMA
+CREATE SCHEMA
+
+> \dn
+       List of schemas
+   Name   |       Owner
+----------+-------------------
+ public   | pg_database_owner
+ schema_a | postgres
+ schema_b | postgres
+ schema_c | postgres
+(4 rows)
+```
+
+Three new schemas get created which we can inspect with `\dn`.
+
+Notice, if we simply execute the primary statement, we can see the intermediate
+result that `\gexec` will subsequently execute.
+
+```sql
+> select
+    'create schema if not exists schema_' || letter || ';'
+  from unnest(array['a', 'b', 'c']) as letter
+  \g
+
+               ?column?
+---------------------------------------
+ create schema if not exists schema_a;
+ create schema if not exists schema_b;
+ create schema if not exists schema_c;
+(3 rows)
+```