function dbDelta( $queries = '', $execute = true ) {
global $wpdb;
if ( in_array( $queries, array( '', 'all', 'blog', 'global', 'ms_global' ), true ) )
$queries = wp_get_db_schema( $queries );
if ( !is_array($queries) ) {
$queries = explode( ';', $queries );
$queries = array_filter( $queries );
}
$queries = apply_filters( 'dbdelta_queries', $queries );
$cqueries = array();
$iqueries = array();
$for_update = array();
foreach ($queries as $qry) {
if ( preg_match( "|CREATE TABLE ([^ ]*)|", $qry, $matches ) ) {
$cqueries[ trim( $matches[1], '`' ) ] = $qry;
$for_update[$matches[1]] = 'Created table '.$matches[1];
} elseif ( preg_match( "|CREATE DATABASE ([^ ]*)|", $qry, $matches ) ) {
array_unshift( $cqueries, $qry );
} elseif ( preg_match( "|INSERT INTO ([^ ]*)|", $qry, $matches ) ) {
$iqueries[] = $qry;
} elseif ( preg_match( "|UPDATE ([^ ]*)|", $qry, $matches ) ) {
$iqueries[] = $qry;
} else {
}
}
$cqueries = apply_filters( 'dbdelta_create_queries', $cqueries );
$iqueries = apply_filters( 'dbdelta_insert_queries', $iqueries );
$text_fields = array( 'tinytext', 'text', 'mediumtext', 'longtext' );
$blob_fields = array( 'tinyblob', 'blob', 'mediumblob', 'longblob' );
$global_tables = $wpdb->tables( 'global' );
foreach ( $cqueries as $table => $qry ) {
if ( in_array( $table, $global_tables ) && ! wp_should_upgrade_global_tables() ) {
unset( $cqueries[ $table ], $for_update[ $table ] );
continue;
}
$suppress = $wpdb->suppress_errors();
$tablefields = $wpdb->get_results("DESCRIBE {$table};");
$wpdb->suppress_errors( $suppress );
if ( ! $tablefields )
continue;
$cfields = $indices = $indices_without_subparts = array();
preg_match("|\((.*)\)|ms", $qry, $match2);
$qryline = trim($match2[1]);
$flds = explode("\n", $qryline);
foreach ( $flds as $fld ) {
$fld = trim( $fld, " \t\n\r\0\x0B," );
preg_match( '|^([^ ]*)|', $fld, $fvals );
$fieldname = trim( $fvals[1], '`' );
$fieldname_lowercased = strtolower( $fieldname );
$validfield = true;
switch ( $fieldname_lowercased ) {
case '':
case 'primary':
case 'index':
case 'fulltext':
case 'unique':
case 'key':
case 'spatial':
$validfield = false;
preg_match(
'/^'
. '(?P<index_type>'
. 'PRIMARY\s+KEY|(?:UNIQUE|FULLTEXT|SPATIAL)\s+(?:KEY|INDEX)|KEY|INDEX'
. ')'
. '\s+'
. '(?:'
. '`?'
. '(?P<index_name>'
. '(?:[0-9a-zA-Z$_-]|[\xC2-\xDF][\x80-\xBF])+'
. ')'
. '`?'
. '\s+'
. ')*'
. '\('
. '(?P<index_columns>'
. '.+?'
. ')'
. '\)'
. '$/im',
$fld,
$index_matches
);
$index_type = strtoupper( preg_replace( '/\s+/', ' ', trim( $index_matches['index_type'] ) ) );
$index_type = str_replace( 'INDEX', 'KEY', $index_type );
$index_name = ( 'PRIMARY KEY' === $index_type ) ? '' : '`' . strtolower( $index_matches['index_name'] ) . '`';
$index_columns = $index_columns_without_subparts = array_map( 'trim', explode( ',', $index_matches['index_columns'] ) );
foreach ( $index_columns as $id => &$index_column ) {
preg_match(
'/'
. '`?'
. '(?P<column_name>'
. '(?:[0-9a-zA-Z$_-]|[\xC2-\xDF][\x80-\xBF])+'
. ')'
. '`?'
. '(?:'
. '\s*'
. '\('
. '\s*'
. '(?P<sub_part>'
. '\d+'
. ')'
. '\s*'
. '\)'
. ')?'
. '/',
$index_column,
$index_column_matches
);
$index_column = '`' . $index_column_matches['column_name'] . '`';
$index_columns_without_subparts[ $id ] = $index_column;
if ( isset( $index_column_matches['sub_part'] ) ) {
$index_column .= '(' . $index_column_matches['sub_part'] . ')';
}
}
$indices[] = "{$index_type} {$index_name} (" . implode( ',', $index_columns ) . ")";
$indices_without_subparts[] = "{$index_type} {$index_name} (" . implode( ',', $index_columns_without_subparts ) . ")";
unset( $index_column, $index_column_matches, $index_matches, $index_type, $index_name, $index_columns, $index_columns_without_subparts );
break;
}
if ( $validfield ) {
$cfields[ $fieldname_lowercased ] = $fld;
}
}
foreach ( $tablefields as $tablefield ) {
$tablefield_field_lowercased = strtolower( $tablefield->Field );
$tablefield_type_lowercased = strtolower( $tablefield->Type );
if ( array_key_exists( $tablefield_field_lowercased, $cfields ) ) {
preg_match( '|`?' . $tablefield->Field . '`? ([^ ]*( unsigned)?)|i', $cfields[ $tablefield_field_lowercased ], $matches );
$fieldtype = $matches[1];
$fieldtype_lowercased = strtolower( $fieldtype );
if ($tablefield->Type != $fieldtype) {
$do_change = true;
if ( in_array( $fieldtype_lowercased, $text_fields ) && in_array( $tablefield_type_lowercased, $text_fields ) ) {
if ( array_search( $fieldtype_lowercased, $text_fields ) < array_search( $tablefield_type_lowercased, $text_fields ) ) {
$do_change = false;
}
}
if ( in_array( $fieldtype_lowercased, $blob_fields ) && in_array( $tablefield_type_lowercased, $blob_fields ) ) {
if ( array_search( $fieldtype_lowercased, $blob_fields ) < array_search( $tablefield_type_lowercased, $blob_fields ) ) {
$do_change = false;
}
}
if ( $do_change ) {
$cqueries[] = "ALTER TABLE {$table} CHANGE COLUMN `{$tablefield->Field}` " . $cfields[ $tablefield_field_lowercased ];
$for_update[$table.'.'.$tablefield->Field] = "Changed type of {$table}.{$tablefield->Field} from {$tablefield->Type} to {$fieldtype}";
}
}
if ( preg_match( "| DEFAULT '(.*?)'|i", $cfields[ $tablefield_field_lowercased ], $matches ) ) {
$default_value = $matches[1];
if ($tablefield->Default != $default_value) {
$cqueries[] = "ALTER TABLE {$table} ALTER COLUMN `{$tablefield->Field}` SET DEFAULT '{$default_value}'";
$for_update[$table.'.'.$tablefield->Field] = "Changed default value of {$table}.{$tablefield->Field} from {$tablefield->Default} to {$default_value}";
}
}
unset( $cfields[ $tablefield_field_lowercased ] );
} else {
}
}
foreach ($cfields as $fieldname => $fielddef) {
$cqueries[] = "ALTER TABLE {$table} ADD COLUMN $fielddef";
$for_update[$table.'.'.$fieldname] = 'Added column '.$table.'.'.$fieldname;
}
$tableindices = $wpdb->get_results("SHOW INDEX FROM {$table};");
if ($tableindices) {
$index_ary = array();
foreach ($tableindices as $tableindex) {
$keyname = strtolower( $tableindex->Key_name );
$index_ary[$keyname]['columns'][] = array('fieldname' => $tableindex->Column_name, 'subpart' => $tableindex->Sub_part);
$index_ary[$keyname]['unique'] = ($tableindex->Non_unique == 0)?true:false;
$index_ary[$keyname]['index_type'] = $tableindex->Index_type;
}
foreach ($index_ary as $index_name => $index_data) {
$index_string = '';
if ($index_name == 'primary') {
$index_string .= 'PRIMARY ';
} elseif ( $index_data['unique'] ) {
$index_string .= 'UNIQUE ';
}
if ( 'FULLTEXT' === strtoupper( $index_data['index_type'] ) ) {
$index_string .= 'FULLTEXT ';
}
if ( 'SPATIAL' === strtoupper( $index_data['index_type'] ) ) {
$index_string .= 'SPATIAL ';
}
$index_string .= 'KEY ';
if ( 'primary' !== $index_name ) {
$index_string .= '`' . $index_name . '`';
}
$index_columns = '';
foreach ($index_data['columns'] as $column_data) {
if ( $index_columns != '' ) {
$index_columns .= ',';
}
$index_columns .= '`' . $column_data['fieldname'] . '`';
}
$index_string .= " ($index_columns)";
if ( ! ( ( $aindex = array_search( $index_string, $indices_without_subparts ) ) === false ) ) {
unset( $indices_without_subparts[ $aindex ] );
unset( $indices[ $aindex ] );
}
}
}
foreach ( (array) $indices as $index ) {
$cqueries[] = "ALTER TABLE {$table} ADD $index";
$for_update[] = 'Added index ' . $table . ' ' . $index;
}
unset( $cqueries[ $table ], $for_update[ $table ] );
}
$allqueries = array_merge($cqueries, $iqueries);
if ($execute) {
foreach ($allqueries as $query) {
$wpdb->query($query);
}
}
return $for_update;
}
Contributed by 
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Assuming we’re at the WordPress URL “http://blog.example.com/client/?s=word”… Note the use of
esc_url()before outputting the link. This is necessary because this function does not escape URLs and if output without escaping, would make the page vulnerable to XSS scripting.// This would output '/client/?s=word&foo=bar'echoesc_url( add_query_arg('foo','bar') );// This would output '/client/?s=word&foo=bar&baz=tiny'$arr_params=array('foo'=>'bar','baz'=>'tiny');echoesc_url( add_query_arg($arr_params) );Since
get_permalink()returns a full URL, you could use that when you want to add variables to a post’s page./** This would output whatever the URL to post ID 9 is, with 'hello=there'* appended with either ? or &, depending on what's needed.*/echoesc_url( add_query_arg('hello','there', get_permalink( 9 ) ) );To safely redirect user to a custom page inside
plugins.php// Redirect to Welcome Page.// Redirects to your-domain.com/wp-admin/plugin.php?page=your_plugin_page.wp_safe_redirect( add_query_arg(array('page'=>'your_plugin_page'), admin_url('plugins.php') ) );More often than not you’ll probably find yourself creating URLs using the following method within the page you’re currently on. In these cases you can use the URL you want to affect as the last parameter. The use of
esc_url()is not required here, because the value is known to be safe.// This would output 'http://blog.example.com/2009/04/16/?hello=world'echoesc_url( add_query_arg('hello','world','http://blog.example.com/2009/04/16/') );Removing values and setting via an associative array:
$query='http://example.com/link?foo=bar';$new_query= add_query_arg(array('foo'=> false,'baz'=>'qux'),$query);print($new_query);// http://example.com/link?baz=quxA way to get the current total url using
add_query_arghome_url( add_query_arg( null, null ));