How does sqlserver obtain the names of all tables in a database and the names of all fields in a table?

1. query all database names in the database:

 
 SelectNameFromMaster.. sysdatabasesOrder ByName
 

2. query all the table names in a database:

 
 SelectNameFromSysobjectsWhereXtype='U' Order ByName
 

3. query table structure information:

 1   Select ( Case   When A. colorder =  1   Then D. Name Else   Null   End  ) Table Name,  2   A. colorder FIELD No., A. Name field name,  3 ( Case   When   Columnproperty (A. ID, A. Name, '  Isidentity ' ) =  1   Then   '  √  '  Else   ''   End  ) ID,  4 ( Case   When ( Select   Count (* ) From  Sysobjects  5   Where (Name In ( Select Name From  Sysindexes  6   Where (ID = A. ID) And (Indid In    7 (Select Indid From  Sysindexkeys  8   Where (ID = A. ID) And (Colid In    9 ( Select Colid From Syscolumns Where (ID = A. ID) And (Name=  A. Name )))))))  10   And (Xtype =   '  PK  ' )) >  0   Then   '  √  '   Else   ''   End ) Primary key, B. Name type, A. Length occupies the number of bytes,  11   Columnproperty (A. ID, A. Name, '  Precision  ' ) As  Length,  12   Isnull ( Columnproperty (A. ID, A. Name, '  Scale  ' ), 0 ) As Decimal places ,( Case   When A. isnullable =  1   Then   '  √  '  Else   ''   End  ) Can be empty,  13   Isnull (E. Text ,'' ) Default value, Isnull (G. [  Value  ] , '   ' ) As   [  Description  ]  14   From  Syscolumns  15   Left   Join Policypes B On A. xtype =  B. xusertype  16   Inner   Join Sysobjects d On A. ID = D. id And D. xtype =  '  U  '   And D. Name <> '  Dtproperties  '   17   Left   Join Syscomments E On A. cdefault =  E. ID  18   Left   Join SYS. extended_properties g On A. ID = G. major_id And A. colid=  G. minor_id  19   Left   Join SYS. extended_properties F On D. id = F. Class And F. minor_id =  0  20   Where B. Name Is   Not   Null 21   --  Where D. Name = 'table to be query' -- if only the specified table is queried, add this condition.  22   Order   By A. ID, A. colorder