Index not used in a partitioned Oracle table

I have a table partitioned by list create table ICT_ENCOURS_BRUT ( code_exercice VARCHAR2(4), CODE_PRODUIT VARCHAR2(2), ....... ) partition by list (CODE_EXERCICE) ( partition CODE_EXERCICE_2018 values ('2018') tablespace DATA_BI_PARTITION_2018 , partition CODE_EXERCICE_2019 values ('2019') tablespace DATA_BI_PARTITION_2019 , partition CODE_EXERCICE_2020 values ('2020') tablespace DATA_BI_PARTITION_2020 , partition CODE_EXERCICE_2021 values ('2021') tablespace DATA_BI_PARTITION_2021 ); and i have 2 indexes : CREATE INDEX EKIPIC.IDX_CODE_EXERCICE ON EKIPIC.ICT_ENCOURS_BRUT (CODE_EXERCICE) TABLESPACE INDEX_BI LOGGING LOCAL ( PARTITION CODE_EXERCICE_2018 NOCOMPRESS TABLESPACE INDEX_BI_PARTITION_2018, PARTITION CODE_EXERCICE_2019 NOCOMPRESS TABLESPACE INDEX_BI_PARTITION_2019, PARTITION CODE_EXERCICE_2020 NOCOMPRESS TABLESPACE INDEX_BI_PARTITION_2020, PARTITION CODE_EXERCICE_2021 NOCOMPRESS TABLESPACE INDEX_BI_PARTITION_2021 ) ONLINE; create index IDX_CODE_PRODUIT on ICT_ENCOURS_BRUT (CODE_PRODUIT) tablespace INDEX_BI ; the explain plan show a full scan access when i perform SELECT * from ICT_ENCOURS_BRUT where code_produit='LOA' ----------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost | Time | ----------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 812259 | 242053182 | 32268 | 00:07:32 | | 1 | PARTITION LIST ALL | | 812259 | 242053182 | 32268 | 00:07:32 | | * 2 | TABLE ACCESS FULL | ICT_ENCOURS_BRUT | 812259 | 242053182 | 32268 | 00:07:32 | ----------------------------------------------------------------------------------------- Predicate Information (identified by operation id): ------------------------------------------ * 2 - filter("CODE_PRODUIT"='LOA') the same way when i try to use select * from ICT_ENCOURS_BRUT i where i.code_exercice='2019' Plan Hash Value : 2304474508 -------------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost | Time | -------------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1604226 | 474850896 | 12511 | 00:02:56 | | 1 | PARTITION LIST SINGLE | | 1604226 | 474850896 | 12511 | 00:02:56 | | 2 | TABLE ACCESS FULL | ICT_ENCOURS_BRUT | 1604226 | 474850896 | 12511 | 00:02:56 | -------------------------------------------------------------------------------------------- Why cannot use the indexes assuming that stats is updated?