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MDL-63020 ddl: fix nullable unique indexes in OCI and MS SQL

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This works-around the default non-standard behaviour of these DB engines.
This commit is contained in:
Tim Hunt
2018-09-20 17:41:22 +01:00
parent 54b2b1d27f
commit 5abc431335
5 changed files with 185 additions and 0 deletions
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lib/ddl/oracle_sql_generator.php
+55
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@@ -131,6 +131,61 @@ class oracle_sql_generator extends sql_generator {
return $tablename;
}
public function getCreateIndexSQL($xmldb_table, $xmldb_index) {
if ($error = $xmldb_index->validateDefinition($xmldb_table)) {
throw new coding_exception($error);
}
$indexfields = $this->getEncQuoted($xmldb_index->getFields());
$unique = '';
$suffix = 'ix';
if ($xmldb_index->getUnique()) {
$unique = ' UNIQUE';
$suffix = 'uix';
$nullablefields = $this->get_nullable_fields_in_index($xmldb_table, $xmldb_index);
if ($nullablefields) {
// If this is a unique index with nullable fields, then we have to
// apply the work-around from https://community.oracle.com/message/9518046#9518046.
//
// For example if you have a unique index on the three columns
// (required, option1, option2) where the first one is non-null,
// and the others nullable, then the SQL will end up as
//
// CREATE UNIQUE INDEX index_name ON table_name (
// CASE WHEN option1 IS NOT NULL AND option2 IS NOT NULL THEN required ELSE NULL END,
// CASE WHEN option1 IS NOT NULL AND option2 IS NOT NULL THEN option1 ELSE NULL END,
// CASE WHEN option1 IS NOT NULL AND option2 IS NOT NULL THEN option2 ELSE NULL END)
//
// Basically Oracle behaves according to the standard if either
// none of the columns are NULL or all columns contain NULL. Therefore,
// if any column is NULL, we treat them all as NULL for the index.
$conditions = [];
foreach ($nullablefields as $fieldname) {
$conditions[] = $this->getEncQuoted($fieldname) .
' IS NOT NULL';
}
$condition = implode(' AND ', $conditions);
$updatedindexfields = [];
foreach ($indexfields as $fieldname) {
$updatedindexfields[] = 'CASE WHEN ' . $condition . ' THEN ' .
$fieldname . ' ELSE NULL END';
}
$indexfields = $updatedindexfields;
}
}
$index = 'CREATE' . $unique . ' INDEX ';
$index .= $this->getNameForObject($xmldb_table->getName(), implode(', ', $xmldb_index->getFields()), $suffix);
$index .= ' ON ' . $this->getTableName($xmldb_table);
$index .= ' (' . implode(', ', $indexfields) . ')';
return array($index);
}
/**
* Given one correct xmldb_table, returns the SQL statements
* to create temporary table (inside one array).