Add a boolean "migrate" flag for indexes

This allows to select which indexes should be migrated.
That requires the creation of an otherwise redundant "indexes" table
in the PostgreSQL staging schema.

This closes #22.

Author: laurenz

README.md

@@ -372,6 +372,9 @@ Migration functions
     system schemas are processed.  
     The names must be as they appear in Oracle, which is usually in upper case.
 
+  Indexes are only migrated if the `migrate` flag on the corresponding entries
+  in the `tables` and `indexes` table in the PostgreSQL staging schema are set.
+
   The return value is the number of captured errors that have been turned
   into warnings.
 

TODO

@@ -3,10 +3,6 @@ List of things to do
 
 - Support GENERATED AS IDENTITY with later Oracle versions.
 
-- Create a table "indexes" with a "migrate" column in the PostgreSQL stage
-  to allow excluding certain indexes from the migration.
-  See issue #22.
-
 - Refactor the code to create an abstraction layer that allows migration
   from other databases using other foreign data wrappers.
   This is a hard one.

ora_migrator--0.9.1.sql

@@ -925,6 +925,17 @@ BEGIN
                   staging_schema)
       USING only_schemas;
 
+   /* refresh "indexes" table */
+   INSERT INTO indexes (schema, table_name, index_name, uniqueness)
+      SELECT DISTINCT schema,
+                      table_name,
+                      index_name,
+                      uniqueness
+      FROM index_columns
+   ON CONFLICT ON CONSTRAINT indexes_pkey DO UPDATE SET
+      table_name = EXCLUDED.table_name,
+      uniqueness = EXCLUDED.uniqueness;
+
    /* copy "schemas" table */
    EXECUTE format(E'INSERT INTO schemas (schema)\n'
                    '   SELECT oracle_tolower(schema)\n'
@@ -1207,6 +1218,16 @@ BEGIN
          PRIMARY KEY (schema, index_name, position)
    );
 
+   CREATE TABLE indexes (
+      schema     name    NOT NULL,
+      table_name name    NOT NULL,
+      index_name name    NOT NULL,
+      uniqueness boolean NOT NULL,
+      migrate    boolean NOT NULL DEFAULT TRUE,
+      CONSTRAINT indexes_pkey
+         PRIMARY KEY (schema, index_name)
+   );
+
    CREATE TABLE schemas (
       schema name NOT NULL
          CONSTRAINT schemas_pkey PRIMARY KEY
@@ -2261,11 +2282,14 @@ BEGIN
    FOR loc_s, loc_t, ind_name, uniq, colpos, des, is_expr, expr IN
       SELECT schema, table_name, i.index_name, i.uniqueness, i.position, i.descend, i.is_expression, i.column_name
       FROM index_columns i
+         JOIN indexes ind
+            USING (schema, table_name, index_name)
          JOIN tables t
             USING (schema, table_name)
       WHERE (only_schemas IS NULL
          OR schema =ANY (only_schemas))
         AND t.migrate
+        AND ind.migrate
       ORDER BY schema, table_name, i.index_name, i.position
    LOOP
       IF old_s <> loc_s OR old_t <> loc_t OR old_c <> ind_name THEN