generate postgresql schema in json and then use to convert into mermaid chart. credit https://chartdb.io/

query.sql

WITH fk_info AS (
    SELECT array_to_string(array_agg(CONCAT('{"schema":"', replace(schema_name, '"', ''), '"',
                                            ',"table":"', replace(table_name::text, '"', ''), '"',
                                            ',"column":"', replace(fk_column::text, '"', ''), '"',
                                            ',"foreign_key_name":"', foreign_key_name, '"',
                                            ',"reference_schema":"', COALESCE(replace(reference_schema, '"', ''), 'public'), '"',
                                            ',"reference_table":"', replace(reference_table, '"', ''), '"',
                                            ',"reference_column":"', replace(reference_column, '"', ''), '"',
                                            ',"fk_def":"', replace(fk_def, '"', ''),
                                            '"}')), ',') as fk_metadata
    FROM (
            SELECT c.conname AS foreign_key_name,
                    n.nspname AS schema_name,
                    CASE
                        WHEN position('.' in conrelid::regclass::text) > 0
                        THEN split_part(conrelid::regclass::text, '.', 2)
                        ELSE conrelid::regclass::text
                    END AS table_name,
                    a.attname AS fk_column,
                    nr.nspname AS reference_schema,
                    CASE
                        WHEN position('.' in confrelid::regclass::text) > 0
                        THEN split_part(confrelid::regclass::text, '.', 2)
                        ELSE confrelid::regclass::text
                    END AS reference_table,
                    af.attname AS reference_column,
                    pg_get_constraintdef(c.oid) as fk_def
                FROM
                    pg_constraint AS c
                JOIN
                    pg_attribute AS a ON a.attnum = ANY(c.conkey) AND a.attrelid = c.conrelid
                JOIN
                    pg_class AS cl ON cl.oid = c.conrelid
                JOIN
                    pg_namespace AS n ON n.oid = cl.relnamespace
                JOIN
                    pg_attribute AS af ON af.attnum = ANY(c.confkey) AND af.attrelid = c.confrelid
                JOIN
                    pg_class AS clf ON clf.oid = c.confrelid
                JOIN
                    pg_namespace AS nr ON nr.oid = clf.relnamespace
                WHERE
                    c.contype = 'f'
                    AND connamespace::regnamespace::text NOT IN ('information_schema', 'pg_catalog')
    ) AS x
), pk_info AS (
    SELECT array_to_string(array_agg(CONCAT('{"schema":"', replace(schema_name, '"', ''), '"',
                                            ',"table":"', replace(pk_table, '"', ''), '"',
                                            ',"column":"', replace(pk_column, '"', ''), '"',
                                            ',"pk_def":"', replace(pk_def, '"', ''),
                                            '"}')), ',') AS pk_metadata
    FROM (
            SELECT connamespace::regnamespace::text AS schema_name,
                CASE
                    WHEN strpos(conrelid::regclass::text, '.') > 0
                    THEN split_part(conrelid::regclass::text, '.', 2)
                    ELSE conrelid::regclass::text
                END AS pk_table,
                unnest(string_to_array(substring(pg_get_constraintdef(oid) FROM '\((.*?)\)'), ',')) AS pk_column,
                pg_get_constraintdef(oid) as pk_def
            FROM
              pg_constraint
            WHERE
              contype = 'p'
              AND connamespace::regnamespace::text NOT IN ('information_schema', 'pg_catalog')
    ) AS y
),
indexes_cols AS (
    SELECT  tnsp.nspname                                                                AS schema_name,
        trel.relname                                                                    AS table_name,
            pg_relation_size('"' || tnsp.nspname || '".' || '"' || irel.relname || '"') AS index_size,
            irel.relname                                                                AS index_name,
            am.amname                                                                   AS index_type,
            a.attname                                                                   AS col_name,
            (CASE WHEN i.indisunique = TRUE THEN 'true' ELSE 'false' END)               AS is_unique,
            irel.reltuples                                                              AS cardinality,
            1 + Array_position(i.indkey, a.attnum)                                      AS column_position,
            CASE o.OPTION & 1 WHEN 1 THEN 'DESC' ELSE 'ASC' END                         AS direction
    FROM pg_index AS i
        JOIN pg_class AS trel ON trel.oid = i.indrelid
        JOIN pg_namespace AS tnsp ON trel.relnamespace = tnsp.oid
        JOIN pg_class AS irel ON irel.oid = i.indexrelid
        JOIN pg_am AS am ON irel.relam = am.oid
        CROSS JOIN LATERAL unnest (i.indkey)
        WITH ORDINALITY AS c (colnum, ordinality) LEFT JOIN LATERAL unnest (i.indoption)
        WITH ORDINALITY AS o (option, ordinality)
        ON c.ordinality = o.ordinality JOIN pg_attribute AS a ON trel.oid = a.attrelid AND a.attnum = c.colnum
    WHERE tnsp.nspname NOT LIKE 'pg_%'
    GROUP BY tnsp.nspname, trel.relname, irel.relname, am.amname, i.indisunique, i.indexrelid, irel.reltuples, a.attname, Array_position(i.indkey, a.attnum), o.OPTION, i.indpred
),
cols AS (
    SELECT array_to_string(array_agg(CONCAT('{"schema":"', cols.table_schema,
                                            '","table":"', cols.table_name,
                                            '","name":"', cols.column_name,
                                            '","ordinal_position":', cols.ordinal_position,
                                            ',"type":"', CASE WHEN cols.column_default IS NOT NULL AND cols.column_default LIKE 'nextval(%' THEN
                                                                CASE
                                                                    WHEN LOWER(replace(cols.data_type, '"', '')) = 'smallint' THEN 'smallserial'
                                                                    WHEN LOWER(replace(cols.data_type, '"', '')) = 'integer' THEN 'serial'
                                                                    WHEN LOWER(replace(cols.data_type, '"', '')) = 'bigint' THEN 'bigserial'
                                                                    ELSE LOWER(replace(cols.data_type, '"', ''))
                                                                END
                                                            WHEN cols.data_type = 'ARRAY' THEN
                                                                format_type(pg_type.typelem, NULL)
                                                            WHEN LOWER(replace(cols.data_type, '"', '')) = 'user-defined' THEN
                                                                format_type(pg_type.oid, NULL)
                                                            ELSE
                                                                LOWER(replace(cols.data_type, '"', ''))
                                                        END,
                                            '","character_maximum_length":"', COALESCE(cols.character_maximum_length::text, 'null'),
                                            '","precision":',
                                                CASE
                                                    WHEN cols.data_type = 'numeric' OR cols.data_type = 'decimal'
                                                    THEN CONCAT('{"precision":', COALESCE(cols.numeric_precision::text, 'null'),
                                                                ',"scale":', COALESCE(cols.numeric_scale::text, 'null'), '}')
                                                    ELSE 'null'
                                                END,
                                            ',"nullable":', CASE WHEN (cols.IS_NULLABLE = 'YES') THEN 'true' ELSE 'false' END,
                                            ',"default":"', CASE WHEN cols.column_default IS NOT NULL AND cols.column_default LIKE 'nextval(%' THEN '' ELSE COALESCE(replace(replace(cols.column_default, '"', '\"'), '\x', '\\x'), '') END,
                                            '","collation":"', COALESCE(cols.COLLATION_NAME, ''),
                                            '","comment":"', null,
                                            '","is_identity":', CASE
                                                WHEN cols.is_identity = 'YES' THEN 'true'
                                                WHEN cols.column_default IS NOT NULL AND cols.column_default LIKE 'nextval(%' THEN 'true'
                                                ELSE 'false'
                                            END,
                                            ',"is_array":', CASE
                                                WHEN cols.data_type = 'ARRAY' OR pg_type.typelem > 0 THEN 'true'
                                                ELSE 'false'
                                            END,
                                            '}')), ',') AS cols_metadata
    FROM information_schema.columns cols
    LEFT JOIN pg_catalog.pg_class c
        ON c.relname = cols.table_name
    JOIN pg_catalog.pg_namespace n
        ON n.oid = c.relnamespace AND n.nspname = cols.table_schema
    LEFT JOIN pg_catalog.pg_description dsc
        ON dsc.objoid = c.oid AND dsc.objsubid = cols.ordinal_position
    LEFT JOIN pg_catalog.pg_attribute attr
        ON attr.attrelid = c.oid AND attr.attname = cols.column_name
    LEFT JOIN pg_catalog.pg_type
        ON pg_type.oid = attr.atttypid
    LEFT JOIN pg_catalog.pg_type AS elem_type
        ON elem_type.oid = pg_type.typelem
    WHERE cols.table_schema NOT IN ('information_schema', 'pg_catalog')
), indexes_metadata AS (
    SELECT array_to_string(array_agg(CONCAT('{"schema":"', schema_name,
                                            '","table":"', table_name,
                                            '","name":"', index_name,
                                            '","column":"', replace(col_name :: TEXT, '"', E'"'),
                                            '","index_type":"', index_type,
                                            '","cardinality":', cardinality,
                                            ',"size":', index_size,
                                            ',"unique":', is_unique,
                                            ',"column_position":', column_position,
                                            ',"direction":"', LOWER(direction),
                                            '"}')), ',') AS indexes_metadata
    FROM indexes_cols x 
), tbls AS (
    SELECT array_to_string(array_agg(CONCAT('{',
                        '"schema":"', tbls.TABLE_SCHEMA, '",',
                        '"table":"', tbls.TABLE_NAME, '",',
                        '"rows":', COALESCE((SELECT s.n_live_tup
                                                FROM pg_stat_user_tables s
                                                WHERE tbls.TABLE_SCHEMA = s.schemaname AND tbls.TABLE_NAME = s.relname),
                                                0), ', "type":"', tbls.TABLE_TYPE, '",', '"engine":"",', '"collation":"",',
                        '"comment":"', null,
                        '"}'
                )),
                ',') AS tbls_metadata
        FROM information_schema.tables tbls
        LEFT JOIN pg_catalog.pg_class c ON c.relname = tbls.TABLE_NAME
        JOIN pg_catalog.pg_namespace n ON n.oid = c.relnamespace
                                            AND n.nspname = tbls.TABLE_SCHEMA
        LEFT JOIN pg_catalog.pg_description dsc ON dsc.objoid = c.oid
                                                AND dsc.objsubid = 0
        WHERE tbls.TABLE_SCHEMA NOT IN ('information_schema', 'pg_catalog') 
), config AS (
    SELECT array_to_string(
                      array_agg(CONCAT('{"name":"', conf.name, '","value":"', replace(conf.setting, '"', E'"'), '"}')),
                      ',') AS config_metadata
    FROM pg_settings conf
), views AS (
    SELECT array_to_string(array_agg(CONCAT('{"schema":"', views.schemaname,
                      '","view_name":"', viewname,
                      '","view_definition":""}')),
                      ',') AS views_metadata
    FROM pg_views views
    WHERE views.schemaname NOT IN ('information_schema', 'pg_catalog') 
), custom_types AS (
    SELECT array_to_string(array_agg(type_json), ',') AS custom_types_metadata
    FROM (
        -- ENUM types
        SELECT CONCAT(
            '{"schema":"', n.nspname,
            '","type":"', t.typname,
            '","kind":"enum"',
            ',"values":[', string_agg('"' || e.enumlabel || '"', ',' ORDER BY e.enumsortorder), ']}'
        ) AS type_json
        FROM pg_type t
        JOIN pg_enum e ON t.oid = e.enumtypid
        JOIN pg_namespace n ON n.oid = t.typnamespace
        WHERE n.nspname NOT IN ('pg_catalog', 'information_schema') 
        GROUP BY n.nspname, t.typname

        UNION ALL

        -- COMPOSITE types
        SELECT CONCAT(
            '{"schema":"', schema_name,
            '","type":"', type_name,
            '","kind":"composite"',
            ',"fields":[', fields_json, ']}'
        ) AS type_json
        FROM (
            SELECT
                n.nspname AS schema_name,
                t.typname AS type_name,
                string_agg(
                    CONCAT('{"field":"', a.attname, '","type":"', format_type(a.atttypid, a.atttypmod), '"}'),
                    ',' ORDER BY a.attnum
                ) AS fields_json
            FROM pg_type t
            JOIN pg_namespace n ON n.oid = t.typnamespace
            JOIN pg_class c ON c.oid = t.typrelid
            JOIN pg_attribute a ON a.attrelid = c.oid
            WHERE t.typtype = 'c'
              AND c.relkind = 'c'  -- Only user-defined composite types
              AND a.attnum > 0 AND NOT a.attisdropped
              AND n.nspname NOT IN ('pg_catalog', 'information_schema') 
            GROUP BY n.nspname, t.typname
        ) AS comp
    ) AS all_types
)
SELECT CONCAT('{    "fk_info": [', COALESCE(fk_metadata, ''),
                    '], "pk_info": [', COALESCE(pk_metadata, ''),
                    '], "columns": [', COALESCE(cols_metadata, ''),
                    '], "indexes": [', COALESCE(indexes_metadata, ''),
                    '], "tables":[', COALESCE(tbls_metadata, ''),
                    '], "views":[', COALESCE(views_metadata, ''),
                    '], "custom_types": [', COALESCE(custom_types_metadata, ''),
                    '], "database_name": "', CURRENT_DATABASE(), '', '", "version": "', '',
              '"}') AS metadata_json_to_import
FROM fk_info, pk_info, cols, indexes_metadata, tbls, config, views, custom_types;