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MDL-78016 dml: Add Oracle support for OFFSET ... FETCH clauses

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Since Oracle 12, these statements (providing the same than the
well-known LIMIT clauses in MySQL and PostgreSQL) are available,

Just let's switch to use them, removing the old complex ROWNUM
based queries needed before to provide limits support.
This commit is contained in:
Eloy Lafuente (stronk7) 2023-04-25 09:59:28 +02:00
parent 2e1c6fd43e
commit ff8a9478b2
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GPG Key ID: 53487A05E6228820
1 changed files with 18 additions and 46 deletions
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64
lib/dml/oci_native_moodle_database.php
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@ -705,48 +705,6 @@ class oci_native_moodle_database extends moodle_database {
return $value;
}
/**
* Transforms the sql and params in order to emulate the LIMIT clause available in other DBs
*
* @param string $sql the SQL select query to execute.
* @param array $params array of sql parameters
* @param int $limitfrom return a subset of records, starting at this point (optional, required if $limitnum is set).
* @param int $limitnum return a subset comprising this many records (optional, required if $limitfrom is set).
* @return array with the transformed sql and params updated
*/
private function get_limit_sql($sql, array $params = null, $limitfrom=0, $limitnum=0) {
list($limitfrom, $limitnum) = $this->normalise_limit_from_num($limitfrom, $limitnum);
// TODO: Add the /*+ FIRST_ROWS */ hint if there isn't another hint
if ($limitfrom and $limitnum) {
$sql = "SELECT oracle_o.*
FROM (SELECT oracle_i.*, rownum AS oracle_rownum
FROM ($sql) oracle_i
WHERE rownum <= :oracle_num_rows
) oracle_o
WHERE oracle_rownum > :oracle_skip_rows";
$params['oracle_num_rows'] = $limitfrom + $limitnum;
$params['oracle_skip_rows'] = $limitfrom;
} else if ($limitfrom and !$limitnum) {
$sql = "SELECT oracle_o.*
FROM (SELECT oracle_i.*, rownum AS oracle_rownum
FROM ($sql) oracle_i
) oracle_o
WHERE oracle_rownum > :oracle_skip_rows";
$params['oracle_skip_rows'] = $limitfrom;
} else if (!$limitfrom and $limitnum) {
$sql = "SELECT *
FROM ($sql)
WHERE rownum <= :oracle_num_rows";
$params['oracle_num_rows'] = $limitnum;
}
return array($sql, $params);
}
/**
* This function will handle all the column values before being inserted/updated to DB for Oracle
* installations. This is because the "special feature" of Oracle where the empty string is
@ -1118,9 +1076,16 @@ class oci_native_moodle_database extends moodle_database {
*/
public function get_recordset_sql($sql, array $params=null, $limitfrom=0, $limitnum=0) {
list($sql, $params, $type) = $this->fix_sql_params($sql, $params);
list($limitfrom, $limitnum) = $this->normalise_limit_from_num($limitfrom, $limitnum);
list($rawsql, $params) = $this->get_limit_sql($sql, $params, $limitfrom, $limitnum);
if ($limitfrom) {
$sql .= " OFFSET $limitfrom ROWS";
}
if ($limitnum) {
$sql .= " FETCH NEXT $limitnum ROWS ONLY";
}
list($rawsql, $params, $type) = $this->fix_sql_params($sql, $params);
list($rawsql, $params) = $this->tweak_param_names($rawsql, $params);
$this->query_start($rawsql, $params, SQL_QUERY_SELECT);
@ -1155,9 +1120,16 @@ class oci_native_moodle_database extends moodle_database {
*/
public function get_records_sql($sql, array $params=null, $limitfrom=0, $limitnum=0) {
list($sql, $params, $type) = $this->fix_sql_params($sql, $params);
list($limitfrom, $limitnum) = $this->normalise_limit_from_num($limitfrom, $limitnum);
list($rawsql, $params) = $this->get_limit_sql($sql, $params, $limitfrom, $limitnum);
if ($limitfrom) {
$sql .= " OFFSET $limitfrom ROWS";
}
if ($limitnum) {
$sql .= " FETCH NEXT $limitnum ROWS ONLY";
}
list($rawsql, $params, $type) = $this->fix_sql_params($sql, $params);
list($rawsql, $params) = $this->tweak_param_names($rawsql, $params);
$this->query_start($rawsql, $params, SQL_QUERY_SELECT);