sqlglot.optimizer.qualify_tables

  1import itertools
  2import typing as t
  3
  4from sqlglot import alias, exp
  5from sqlglot._typing import E
  6from sqlglot.helper import csv_reader, name_sequence
  7from sqlglot.optimizer.scope import Scope, traverse_scope
  8from sqlglot.schema import Schema
  9
 10
 11def qualify_tables(
 12    expression: E,
 13    db: t.Optional[str] = None,
 14    catalog: t.Optional[str] = None,
 15    schema: t.Optional[Schema] = None,
 16) -> E:
 17    """
 18    Rewrite sqlglot AST to have fully qualified tables. Additionally, this
 19    replaces "join constructs" (*) by equivalent SELECT * subqueries.
 20
 21    Examples:
 22        >>> import sqlglot
 23        >>> expression = sqlglot.parse_one("SELECT 1 FROM tbl")
 24        >>> qualify_tables(expression, db="db").sql()
 25        'SELECT 1 FROM db.tbl AS tbl'
 26        >>>
 27        >>> expression = sqlglot.parse_one("SELECT * FROM (tbl1 JOIN tbl2 ON id1 = id2)")
 28        >>> qualify_tables(expression).sql()
 29        'SELECT * FROM (SELECT * FROM tbl1 AS tbl1 JOIN tbl2 AS tbl2 ON id1 = id2) AS _q_0'
 30
 31    Args:
 32        expression: Expression to qualify
 33        db: Database name
 34        catalog: Catalog name
 35        schema: A schema to populate
 36
 37    Returns:
 38        The qualified expression.
 39
 40    (*) See section 7.2.1.2 in https://www.postgresql.org/docs/current/queries-table-expressions.html
 41    """
 42    next_alias_name = name_sequence("_q_")
 43
 44    for scope in traverse_scope(expression):
 45        for derived_table in itertools.chain(scope.ctes, scope.derived_tables):
 46            # Expand join construct
 47            if isinstance(derived_table, exp.Subquery):
 48                unnested = derived_table.unnest()
 49                if isinstance(unnested, exp.Table):
 50                    derived_table.this.replace(exp.select("*").from_(unnested.copy(), copy=False))
 51
 52            if not derived_table.args.get("alias"):
 53                alias_ = next_alias_name()
 54                derived_table.set("alias", exp.TableAlias(this=exp.to_identifier(alias_)))
 55                scope.rename_source(None, alias_)
 56
 57            pivots = derived_table.args.get("pivots")
 58            if pivots and not pivots[0].alias:
 59                pivots[0].set("alias", exp.TableAlias(this=exp.to_identifier(next_alias_name())))
 60
 61        for name, source in scope.sources.items():
 62            if isinstance(source, exp.Table):
 63                if isinstance(source.this, exp.Identifier):
 64                    if not source.args.get("db"):
 65                        source.set("db", exp.to_identifier(db))
 66                    if not source.args.get("catalog"):
 67                        source.set("catalog", exp.to_identifier(catalog))
 68
 69                if not source.alias:
 70                    source = source.replace(
 71                        alias(
 72                            source,
 73                            name or source.name or next_alias_name(),
 74                            copy=True,
 75                            table=True,
 76                        )
 77                    )
 78
 79                pivots = source.args.get("pivots")
 80                if pivots and not pivots[0].alias:
 81                    pivots[0].set(
 82                        "alias", exp.TableAlias(this=exp.to_identifier(next_alias_name()))
 83                    )
 84
 85                if schema and isinstance(source.this, exp.ReadCSV):
 86                    with csv_reader(source.this) as reader:
 87                        header = next(reader)
 88                        columns = next(reader)
 89                        schema.add_table(
 90                            source, {k: type(v).__name__ for k, v in zip(header, columns)}
 91                        )
 92            elif isinstance(source, Scope) and source.is_udtf:
 93                udtf = source.expression
 94                table_alias = udtf.args.get("alias") or exp.TableAlias(
 95                    this=exp.to_identifier(next_alias_name())
 96                )
 97                udtf.set("alias", table_alias)
 98
 99                if not table_alias.name:
100                    table_alias.set("this", exp.to_identifier(next_alias_name()))
101                if isinstance(udtf, exp.Values) and not table_alias.columns:
102                    for i, e in enumerate(udtf.expressions[0].expressions):
103                        table_alias.append("columns", exp.to_identifier(f"_col_{i}"))
104
105    return expression