sqlglot.optimizer.merge_subqueries
1from collections import defaultdict 2 3from sqlglot import expressions as exp 4from sqlglot.helper import find_new_name 5from sqlglot.optimizer.scope import Scope, traverse_scope 6 7 8def merge_subqueries(expression, leave_tables_isolated=False): 9 """ 10 Rewrite sqlglot AST to merge derived tables into the outer query. 11 12 This also merges CTEs if they are selected from only once. 13 14 Example: 15 >>> import sqlglot 16 >>> expression = sqlglot.parse_one("SELECT a FROM (SELECT x.a FROM x) CROSS JOIN y") 17 >>> merge_subqueries(expression).sql() 18 'SELECT x.a FROM x CROSS JOIN y' 19 20 If `leave_tables_isolated` is True, this will not merge inner queries into outer 21 queries if it would result in multiple table selects in a single query: 22 >>> expression = sqlglot.parse_one("SELECT a FROM (SELECT x.a FROM x) CROSS JOIN y") 23 >>> merge_subqueries(expression, leave_tables_isolated=True).sql() 24 'SELECT a FROM (SELECT x.a FROM x) CROSS JOIN y' 25 26 Inspired by https://dev.mysql.com/doc/refman/8.0/en/derived-table-optimization.html 27 28 Args: 29 expression (sqlglot.Expression): expression to optimize 30 leave_tables_isolated (bool): 31 Returns: 32 sqlglot.Expression: optimized expression 33 """ 34 expression = merge_ctes(expression, leave_tables_isolated) 35 expression = merge_derived_tables(expression, leave_tables_isolated) 36 return expression 37 38 39# If a derived table has these Select args, it can't be merged 40UNMERGABLE_ARGS = set(exp.Select.arg_types) - { 41 "expressions", 42 "from", 43 "joins", 44 "where", 45 "order", 46 "hint", 47} 48 49 50# Projections in the outer query that are instances of these types can be replaced 51# without getting wrapped in parentheses, because the precedence won't be altered. 52SAFE_TO_REPLACE_UNWRAPPED = ( 53 exp.Column, 54 exp.EQ, 55 exp.Func, 56 exp.NEQ, 57 exp.Paren, 58) 59 60 61def merge_ctes(expression, leave_tables_isolated=False): 62 scopes = traverse_scope(expression) 63 64 # All places where we select from CTEs. 65 # We key on the CTE scope so we can detect CTES that are selected from multiple times. 66 cte_selections = defaultdict(list) 67 for outer_scope in scopes: 68 for table, inner_scope in outer_scope.selected_sources.values(): 69 if isinstance(inner_scope, Scope) and inner_scope.is_cte: 70 cte_selections[id(inner_scope)].append( 71 ( 72 outer_scope, 73 inner_scope, 74 table, 75 ) 76 ) 77 78 singular_cte_selections = [v[0] for k, v in cte_selections.items() if len(v) == 1] 79 for outer_scope, inner_scope, table in singular_cte_selections: 80 from_or_join = table.find_ancestor(exp.From, exp.Join) 81 if _mergeable(outer_scope, inner_scope, leave_tables_isolated, from_or_join): 82 alias = table.alias_or_name 83 _rename_inner_sources(outer_scope, inner_scope, alias) 84 _merge_from(outer_scope, inner_scope, table, alias) 85 _merge_expressions(outer_scope, inner_scope, alias) 86 _merge_joins(outer_scope, inner_scope, from_or_join) 87 _merge_where(outer_scope, inner_scope, from_or_join) 88 _merge_order(outer_scope, inner_scope) 89 _merge_hints(outer_scope, inner_scope) 90 _pop_cte(inner_scope) 91 outer_scope.clear_cache() 92 return expression 93 94 95def merge_derived_tables(expression, leave_tables_isolated=False): 96 for outer_scope in traverse_scope(expression): 97 for subquery in outer_scope.derived_tables: 98 from_or_join = subquery.find_ancestor(exp.From, exp.Join) 99 alias = subquery.alias_or_name 100 inner_scope = outer_scope.sources[alias] 101 if _mergeable(outer_scope, inner_scope, leave_tables_isolated, from_or_join): 102 _rename_inner_sources(outer_scope, inner_scope, alias) 103 _merge_from(outer_scope, inner_scope, subquery, alias) 104 _merge_expressions(outer_scope, inner_scope, alias) 105 _merge_joins(outer_scope, inner_scope, from_or_join) 106 _merge_where(outer_scope, inner_scope, from_or_join) 107 _merge_order(outer_scope, inner_scope) 108 _merge_hints(outer_scope, inner_scope) 109 outer_scope.clear_cache() 110 return expression 111 112 113def _mergeable(outer_scope, inner_scope, leave_tables_isolated, from_or_join): 114 """ 115 Return True if `inner_select` can be merged into outer query. 116 117 Args: 118 outer_scope (Scope) 119 inner_scope (Scope) 120 leave_tables_isolated (bool) 121 from_or_join (exp.From|exp.Join) 122 Returns: 123 bool: True if can be merged 124 """ 125 inner_select = inner_scope.expression.unnest() 126 127 def _is_a_window_expression_in_unmergable_operation(): 128 window_expressions = inner_select.find_all(exp.Window) 129 window_alias_names = {window.parent.alias_or_name for window in window_expressions} 130 inner_select_name = inner_select.parent.alias_or_name 131 unmergable_window_columns = [ 132 column 133 for column in outer_scope.columns 134 if column.find_ancestor( 135 exp.Where, exp.Group, exp.Order, exp.Join, exp.Having, exp.AggFunc 136 ) 137 ] 138 window_expressions_in_unmergable = [ 139 column 140 for column in unmergable_window_columns 141 if column.table == inner_select_name and column.name in window_alias_names 142 ] 143 return any(window_expressions_in_unmergable) 144 145 def _outer_select_joins_on_inner_select_join(): 146 """ 147 All columns from the inner select in the ON clause must be from the first FROM table. 148 149 That is, this can be merged: 150 SELECT * FROM x JOIN (SELECT y.a AS a FROM y JOIN z) AS q ON x.a = q.a 151 ^^^ ^ 152 But this can't: 153 SELECT * FROM x JOIN (SELECT z.a AS a FROM y JOIN z) AS q ON x.a = q.a 154 ^^^ ^ 155 """ 156 if not isinstance(from_or_join, exp.Join): 157 return False 158 159 alias = from_or_join.alias_or_name 160 161 on = from_or_join.args.get("on") 162 if not on: 163 return False 164 selections = [c.name for c in on.find_all(exp.Column) if c.table == alias] 165 inner_from = inner_scope.expression.args.get("from") 166 if not inner_from: 167 return False 168 inner_from_table = inner_from.alias_or_name 169 inner_projections = {s.alias_or_name: s for s in inner_scope.selects} 170 return any( 171 col.table != inner_from_table 172 for selection in selections 173 for col in inner_projections[selection].find_all(exp.Column) 174 ) 175 176 return ( 177 isinstance(outer_scope.expression, exp.Select) 178 and isinstance(inner_select, exp.Select) 179 and not any(inner_select.args.get(arg) for arg in UNMERGABLE_ARGS) 180 and inner_select.args.get("from") 181 and not outer_scope.pivots 182 and not any(e.find(exp.AggFunc, exp.Select) for e in inner_select.expressions) 183 and not (leave_tables_isolated and len(outer_scope.selected_sources) > 1) 184 and not ( 185 isinstance(from_or_join, exp.Join) 186 and inner_select.args.get("where") 187 and from_or_join.side in {"FULL", "LEFT", "RIGHT"} 188 ) 189 and not ( 190 isinstance(from_or_join, exp.From) 191 and inner_select.args.get("where") 192 and any( 193 j.side in {"FULL", "RIGHT"} for j in outer_scope.expression.args.get("joins", []) 194 ) 195 ) 196 and not _outer_select_joins_on_inner_select_join() 197 and not _is_a_window_expression_in_unmergable_operation() 198 ) 199 200 201def _rename_inner_sources(outer_scope, inner_scope, alias): 202 """ 203 Renames any sources in the inner query that conflict with names in the outer query. 204 205 Args: 206 outer_scope (sqlglot.optimizer.scope.Scope) 207 inner_scope (sqlglot.optimizer.scope.Scope) 208 alias (str) 209 """ 210 taken = set(outer_scope.selected_sources) 211 conflicts = taken.intersection(set(inner_scope.selected_sources)) 212 conflicts -= {alias} 213 214 for conflict in conflicts: 215 new_name = find_new_name(taken, conflict) 216 217 source, _ = inner_scope.selected_sources[conflict] 218 new_alias = exp.to_identifier(new_name) 219 220 if isinstance(source, exp.Subquery): 221 source.set("alias", exp.TableAlias(this=new_alias)) 222 elif isinstance(source, exp.Table) and source.alias: 223 source.set("alias", new_alias) 224 elif isinstance(source, exp.Table): 225 source.replace(exp.alias_(source, new_alias)) 226 227 for column in inner_scope.source_columns(conflict): 228 column.set("table", exp.to_identifier(new_name)) 229 230 inner_scope.rename_source(conflict, new_name) 231 232 233def _merge_from(outer_scope, inner_scope, node_to_replace, alias): 234 """ 235 Merge FROM clause of inner query into outer query. 236 237 Args: 238 outer_scope (sqlglot.optimizer.scope.Scope) 239 inner_scope (sqlglot.optimizer.scope.Scope) 240 node_to_replace (exp.Subquery|exp.Table) 241 alias (str) 242 """ 243 new_subquery = inner_scope.expression.args["from"].this 244 node_to_replace.replace(new_subquery) 245 for join_hint in outer_scope.join_hints: 246 tables = join_hint.find_all(exp.Table) 247 for table in tables: 248 if table.alias_or_name == node_to_replace.alias_or_name: 249 table.set("this", exp.to_identifier(new_subquery.alias_or_name)) 250 outer_scope.remove_source(alias) 251 outer_scope.add_source( 252 new_subquery.alias_or_name, inner_scope.sources[new_subquery.alias_or_name] 253 ) 254 255 256def _merge_joins(outer_scope, inner_scope, from_or_join): 257 """ 258 Merge JOIN clauses of inner query into outer query. 259 260 Args: 261 outer_scope (sqlglot.optimizer.scope.Scope) 262 inner_scope (sqlglot.optimizer.scope.Scope) 263 from_or_join (exp.From|exp.Join) 264 """ 265 266 new_joins = [] 267 268 joins = inner_scope.expression.args.get("joins") or [] 269 for join in joins: 270 new_joins.append(join) 271 outer_scope.add_source(join.alias_or_name, inner_scope.sources[join.alias_or_name]) 272 273 if new_joins: 274 outer_joins = outer_scope.expression.args.get("joins", []) 275 276 # Maintain the join order 277 if isinstance(from_or_join, exp.From): 278 position = 0 279 else: 280 position = outer_joins.index(from_or_join) + 1 281 outer_joins[position:position] = new_joins 282 283 outer_scope.expression.set("joins", outer_joins) 284 285 286def _merge_expressions(outer_scope, inner_scope, alias): 287 """ 288 Merge projections of inner query into outer query. 289 290 Args: 291 outer_scope (sqlglot.optimizer.scope.Scope) 292 inner_scope (sqlglot.optimizer.scope.Scope) 293 alias (str) 294 """ 295 # Collect all columns that reference the alias of the inner query 296 outer_columns = defaultdict(list) 297 for column in outer_scope.columns: 298 if column.table == alias: 299 outer_columns[column.name].append(column) 300 301 # Replace columns with the projection expression in the inner query 302 for expression in inner_scope.expression.expressions: 303 projection_name = expression.alias_or_name 304 if not projection_name: 305 continue 306 columns_to_replace = outer_columns.get(projection_name, []) 307 308 expression = expression.unalias() 309 must_wrap_expression = not isinstance(expression, SAFE_TO_REPLACE_UNWRAPPED) 310 311 for column in columns_to_replace: 312 # Ensures we don't alter the intended operator precedence if there's additional 313 # context surrounding the outer expression (i.e. it's not a simple projection). 314 if isinstance(column.parent, (exp.Unary, exp.Binary)) and must_wrap_expression: 315 expression = exp.paren(expression, copy=False) 316 317 column.replace(expression.copy()) 318 319 320def _merge_where(outer_scope, inner_scope, from_or_join): 321 """ 322 Merge WHERE clause of inner query into outer query. 323 324 Args: 325 outer_scope (sqlglot.optimizer.scope.Scope) 326 inner_scope (sqlglot.optimizer.scope.Scope) 327 from_or_join (exp.From|exp.Join) 328 """ 329 where = inner_scope.expression.args.get("where") 330 if not where or not where.this: 331 return 332 333 expression = outer_scope.expression 334 335 if isinstance(from_or_join, exp.Join): 336 # Merge predicates from an outer join to the ON clause 337 # if it only has columns that are already joined 338 from_ = expression.args.get("from") 339 sources = {from_.alias_or_name} if from_ else {} 340 341 for join in expression.args["joins"]: 342 source = join.alias_or_name 343 sources.add(source) 344 if source == from_or_join.alias_or_name: 345 break 346 347 if exp.column_table_names(where.this) <= sources: 348 from_or_join.on(where.this, copy=False) 349 from_or_join.set("on", from_or_join.args.get("on")) 350 return 351 352 expression.where(where.this, copy=False) 353 354 355def _merge_order(outer_scope, inner_scope): 356 """ 357 Merge ORDER clause of inner query into outer query. 358 359 Args: 360 outer_scope (sqlglot.optimizer.scope.Scope) 361 inner_scope (sqlglot.optimizer.scope.Scope) 362 """ 363 if ( 364 any( 365 outer_scope.expression.args.get(arg) for arg in ["group", "distinct", "having", "order"] 366 ) 367 or len(outer_scope.selected_sources) != 1 368 or any(expression.find(exp.AggFunc) for expression in outer_scope.expression.expressions) 369 ): 370 return 371 372 outer_scope.expression.set("order", inner_scope.expression.args.get("order")) 373 374 375def _merge_hints(outer_scope, inner_scope): 376 inner_scope_hint = inner_scope.expression.args.get("hint") 377 if not inner_scope_hint: 378 return 379 outer_scope_hint = outer_scope.expression.args.get("hint") 380 if outer_scope_hint: 381 for hint_expression in inner_scope_hint.expressions: 382 outer_scope_hint.append("expressions", hint_expression) 383 else: 384 outer_scope.expression.set("hint", inner_scope_hint) 385 386 387def _pop_cte(inner_scope): 388 """ 389 Remove CTE from the AST. 390 391 Args: 392 inner_scope (sqlglot.optimizer.scope.Scope) 393 """ 394 cte = inner_scope.expression.parent 395 with_ = cte.parent 396 if len(with_.expressions) == 1: 397 with_.pop() 398 else: 399 cte.pop()
def
merge_subqueries(expression, leave_tables_isolated=False):
9def merge_subqueries(expression, leave_tables_isolated=False): 10 """ 11 Rewrite sqlglot AST to merge derived tables into the outer query. 12 13 This also merges CTEs if they are selected from only once. 14 15 Example: 16 >>> import sqlglot 17 >>> expression = sqlglot.parse_one("SELECT a FROM (SELECT x.a FROM x) CROSS JOIN y") 18 >>> merge_subqueries(expression).sql() 19 'SELECT x.a FROM x CROSS JOIN y' 20 21 If `leave_tables_isolated` is True, this will not merge inner queries into outer 22 queries if it would result in multiple table selects in a single query: 23 >>> expression = sqlglot.parse_one("SELECT a FROM (SELECT x.a FROM x) CROSS JOIN y") 24 >>> merge_subqueries(expression, leave_tables_isolated=True).sql() 25 'SELECT a FROM (SELECT x.a FROM x) CROSS JOIN y' 26 27 Inspired by https://dev.mysql.com/doc/refman/8.0/en/derived-table-optimization.html 28 29 Args: 30 expression (sqlglot.Expression): expression to optimize 31 leave_tables_isolated (bool): 32 Returns: 33 sqlglot.Expression: optimized expression 34 """ 35 expression = merge_ctes(expression, leave_tables_isolated) 36 expression = merge_derived_tables(expression, leave_tables_isolated) 37 return expression
Rewrite sqlglot AST to merge derived tables into the outer query.
This also merges CTEs if they are selected from only once.
Example:
>>> import sqlglot >>> expression = sqlglot.parse_one("SELECT a FROM (SELECT x.a FROM x) CROSS JOIN y") >>> merge_subqueries(expression).sql() 'SELECT x.a FROM x CROSS JOIN y'
If leave_tables_isolated
is True, this will not merge inner queries into outer
queries if it would result in multiple table selects in a single query:
expression = sqlglot.parse_one("SELECT a FROM (SELECT x.a FROM x) CROSS JOIN y") merge_subqueries(expression, leave_tables_isolated=True).sql() 'SELECT a FROM (SELECT x.a FROM x) CROSS JOIN y'
Inspired by https://dev.mysql.com/doc/refman/8.0/en/derived-table-optimization.html
Arguments:
- expression (sqlglot.Expression): expression to optimize
- leave_tables_isolated (bool):
Returns:
sqlglot.Expression: optimized expression
UNMERGABLE_ARGS =
{'sample', 'group', 'having', 'windows', 'offset', 'into', 'qualify', 'pivots', 'match', 'laterals', 'settings', 'cluster', 'format', 'limit', 'distinct', 'locks', 'distribute', 'with', 'kind', 'sort'}
SAFE_TO_REPLACE_UNWRAPPED =
(<class 'sqlglot.expressions.Column'>, <class 'sqlglot.expressions.EQ'>, <class 'sqlglot.expressions.Func'>, <class 'sqlglot.expressions.NEQ'>, <class 'sqlglot.expressions.Paren'>)
def
merge_ctes(expression, leave_tables_isolated=False):
62def merge_ctes(expression, leave_tables_isolated=False): 63 scopes = traverse_scope(expression) 64 65 # All places where we select from CTEs. 66 # We key on the CTE scope so we can detect CTES that are selected from multiple times. 67 cte_selections = defaultdict(list) 68 for outer_scope in scopes: 69 for table, inner_scope in outer_scope.selected_sources.values(): 70 if isinstance(inner_scope, Scope) and inner_scope.is_cte: 71 cte_selections[id(inner_scope)].append( 72 ( 73 outer_scope, 74 inner_scope, 75 table, 76 ) 77 ) 78 79 singular_cte_selections = [v[0] for k, v in cte_selections.items() if len(v) == 1] 80 for outer_scope, inner_scope, table in singular_cte_selections: 81 from_or_join = table.find_ancestor(exp.From, exp.Join) 82 if _mergeable(outer_scope, inner_scope, leave_tables_isolated, from_or_join): 83 alias = table.alias_or_name 84 _rename_inner_sources(outer_scope, inner_scope, alias) 85 _merge_from(outer_scope, inner_scope, table, alias) 86 _merge_expressions(outer_scope, inner_scope, alias) 87 _merge_joins(outer_scope, inner_scope, from_or_join) 88 _merge_where(outer_scope, inner_scope, from_or_join) 89 _merge_order(outer_scope, inner_scope) 90 _merge_hints(outer_scope, inner_scope) 91 _pop_cte(inner_scope) 92 outer_scope.clear_cache() 93 return expression
def
merge_derived_tables(expression, leave_tables_isolated=False):
96def merge_derived_tables(expression, leave_tables_isolated=False): 97 for outer_scope in traverse_scope(expression): 98 for subquery in outer_scope.derived_tables: 99 from_or_join = subquery.find_ancestor(exp.From, exp.Join) 100 alias = subquery.alias_or_name 101 inner_scope = outer_scope.sources[alias] 102 if _mergeable(outer_scope, inner_scope, leave_tables_isolated, from_or_join): 103 _rename_inner_sources(outer_scope, inner_scope, alias) 104 _merge_from(outer_scope, inner_scope, subquery, alias) 105 _merge_expressions(outer_scope, inner_scope, alias) 106 _merge_joins(outer_scope, inner_scope, from_or_join) 107 _merge_where(outer_scope, inner_scope, from_or_join) 108 _merge_order(outer_scope, inner_scope) 109 _merge_hints(outer_scope, inner_scope) 110 outer_scope.clear_cache() 111 return expression