The INFORMATION_SCHEMA INNODB_INDEXES Table An identifier for the index. Index identifiers are unique across all the databases in an instance. • NAME • TABLE_ID • TYPE • N_FIELDS • PAGE_NO • MERGE_THRESHOLD • SPACE The root page number of the index B-tree. For full-text indexes, the  PAGE_NO  column is unused and set to -1 ( FIL_NULL ) because the full-text index is laid out in several B-trees (auxiliary tables). An identifier for the tablespace where the index resides. 0 means the  InnoDB  system tablespace. Any other number represents a table created with a separate  .ibd  file in file-per-table mode. This identifier stays the same after a  TRUNCATE TABLE  statement. Because all indexes for a table reside in the same tablespace as the table, this value is not necessarily unique. The merge threshold value for index pages. If the amount of data in an index page falls below the MERGE_THRESHOLD  value when a row is deleted or when a row is shortened by an update operation, InnoDB  attempts to merge the index page with the neighboring index page. The default threshold value is 50%. For more information, see Section 15.8.11, “Configuring the Merge Threshold for Index Pages” . The number of columns in the index key. For  GEN_CLUST_INDEX  indexes, this value is 0 because the index is created using an artificial value rather than a real table column. A numeric value derived from bit-level information that identifies the index type. 0 = nonunique secondary index; 1 = automatically generated clustered index ( GEN_CLUST_INDEX ); 2 = unique nonclustered index; 3 = clustered index; 32 = full-text index; 64 = spatial index; 128 = secondary index on a virtual generated column. An identifier representing the table associated with the index; the same value as INNODB_TABLES.TABLE_ID . The name of the index. Most indexes created implicitly by  InnoDB  have consistent names but the index names are not necessarily unique. Examples:  PRIMARY  for a primary key index,  GEN_CLUST_INDEX  for the index representing a primary key when one is not specified, and  ID_IND ,  FOR_IND , and  REF_IND for foreign key constraints. Example 4869 mysql>  SELECT * FROM INFORMATION_SCHEMA.INNODB_INDEXES WHERE TABLE_ID = 34\G *************************** 1. row *************************** INDEX_ID: 39 NAME: GEN_CLUST_INDEX TABLE_ID: 34 TYPE: 1 N_FIELDS: 0 PAGE_NO: 3 SPACE: 23 MERGE_THRESHOLD: 50 *************************** 2. row ***************************