Get schema All tables && get all fields of a table

Note: The following is PostgreSQL, the other database skips \d[+] table_name View "detailed" Table structure

To get all the tables under a schame, or to get all the fields for a table, you need to rely on both tables:
Information_schema.tables and information_schema.columns The first table holds information for all tables under all schemas

\d information_schema.tables View "Information_schema.tables" Column | Type | Modifiers------------------------------+-----------------------------------+-----------Table_catalog | 
 Information_schema.sql_identifier | Table_schema | 
 Information_schema.sql_identifier | table_name | 
 Information_schema.sql_identifier | Table_type | 
 Information_schema.character_data | Self_referencing_column_name | 
 Information_schema.sql_identifier | reference_generation | 
 Information_schema.character_data | User_defined_type_catalog | 
 Information_schema.sql_identifier | User_defined_type_schema | 
 Information_schema.sql_identifier | User_defined_type_name | 
 Information_schema.sql_identifier | Is_insertable_into | 
 Information_schema.yes_or_no | is_typed |      Information_schema.yes_or_no| commit_action |  Information_schema.character_data |

The second table is the name of the field that holds all the tables under all schemas

\d information_schema.columns View "Information_schema.columns" Column | Type | Modifiers--------------------------+------------------------------------+-----------Table_catalog | 
 Information_schema.sql_identifier | Table_schema | 
 Information_schema.sql_identifier | table_name | 
 Information_schema.sql_identifier | column_name | 
 Information_schema.sql_identifier | ordinal_position | 
 Information_schema.cardinal_number | Column_default | 
 Information_schema.character_data | is_nullable | 
 Information_schema.yes_or_no | Data_type | 
 Information_schema.character_data | Character_maximum_length | 
 Information_schema.cardinal_number | Character_octet_length | 
 Information_schema.cardinal_number | numeric_precision | 
 Information_schema.cardinal_number | Numeric_precision_radix | InformatiOn_schema.cardinal_number | Numeric_scale | 
 Information_schema.cardinal_number | datetime_precision | 
 Information_schema.cardinal_number | Interval_type | 
 Information_schema.character_data | interval_precision | 
 Information_schema.cardinal_number | Character_set_catalog | 
 Information_schema.sql_identifier | Character_set_schema | 
 Information_schema.sql_identifier | Character_set_name | 
 Information_schema.sql_identifier | Collation_catalog | 
 Information_schema.sql_identifier | Collation_schema | 
 Information_schema.sql_identifier | Collation_name | 
 Information_schema.sql_identifier | Domain_catalog | 
 Information_schema.sql_identifier | Domain_schema | 
 Information_schema.sql_identifier | domain_name | 
 Information_schema.sql_identifier | Udt_catalog | 
 Information_schema.sql_identifier | Udt_schema | Information_schema.Sql_identifier | Udt_name | 
 Information_schema.sql_identifier | Scope_catalog | 
 Information_schema.sql_identifier | Scope_schema | 
 Information_schema.sql_identifier | Scope_name | 
 Information_schema.sql_identifier | maximum_cardinality | 
 Information_schema.cardinal_number | Dtd_identifier | 
 Information_schema.sql_identifier | is_self_referencing | 
 Information_schema.yes_or_no | is_identity | 
 Information_schema.yes_or_no | identity_generation | 
 Information_schema.character_data | Identity_start | 
 Information_schema.character_data | identity_increment | 
 Information_schema.character_data | Identity_maximum | 
 Information_schema.character_data | Identity_minimum | 
 Information_schema.character_data | identity_cycle | 
 Information_schema.yes_or_no | is_generated | Information_schema.character_Data | generation_expression | 
 Information_schema.character_data | is_updatable | 
 Information_schema.yes_or_no |

According to the fields of these two tables, it becomes easy to get all the tables of a schema and get all the fields of a table. get all the tables under a schame:

Select table_name from information_schema.tables where table_schema= ' schema_name ' and table_type= ' table_name ';

get all fields of a table

Select column_name from Information_schema.columns where table_schema= ' schema_name ' and table_name= ' table_name '

get a field that holds text for a table

Select Column_name,data_type from Information_schema.columns where table_schema= ' Table_schema ' and Table_name= ' Table_ Name ' and data_type in (' character varying ', ' text ');