Add Ignore Duplicates When Inserting Records as a MySQL TIL

README.md

@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
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-_1319 TILs and counting..._
+_1320 TILs and counting..._
 
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@@ -554,6 +554,7 @@ _1319 TILs and counting..._
 - [Display Output In A Vertical Format](mysql/display-output-in-a-vertical-format.md)
 - [Doing Date Math](mysql/doing-date-math.md)
 - [Dump A Database To A File](mysql/dump-a-database-to-a-file.md)
+- [Ignore Duplicates When Inserting Records](mysql/ignore-duplicates-when-inserting-records.md)
 - [List Databases And Tables](mysql/list-databases-and-tables.md)
 - [Show Create Statement For A Table](mysql/show-create-statement-for-a-table.md)
 - [Show Tables That Match A Pattern](mysql/show-tables-that-match-a-pattern.md)

mysql/ignore-duplicates-when-inserting-records.md

@@ -0,0 +1,34 @@
+# Ignore Duplicates When Inserting Records
+
+While trying to run a seed script to set up some application data in a MySQL
+database, I ran into several duplicate-key errors. Some of this data had
+already been added in another context, but I still need some of the seeds.
+
+```sql
+insert into MerchantAccount (col1, col2, col3)
+  values ('data1', 'data2', 'data3'),
+         ('data4', 'data5', 'data6'),
+         (...);
+```
+
+The solution was to allow MySQL to `ignore` the duplicate records and insert
+the rest.
+
+```sql
+insert ignore into MerchantAccount (col1, col2, col3)
+  values ('data1', 'data2', 'data3'),
+         ('data4', 'data5', 'data6'),
+         (...);
+```
+
+Notice all I had to do was update the statment by adding `ignore` right after
+`insert.`
+
+> If you use the `IGNORE` modifier, ignorable errors that occur while executing
+> the `INSERT` statement are ignored. For example, without `IGNORE`, a row that
+> duplicates an existing `UNIQUE` index or `PRIMARY KEY` value in the table
+> causes a duplicate-key error and the statement is aborted. With `IGNORE`, the
+> row is discarded and no error occurs. Ignored errors generate warnings
+> instead.
+
+[source](https://dev.mysql.com/doc/refman/8.0/en/insert.html)