Django：Postgresql BTree索引

使用db_index参数创建btree索引，当字段类型是varchar或text时会额外创建like index， 具体参见：DatabaseSchemaEditor._create_like_index_sql：

class BTreeIdx(models.Model):
    content = models.CharField(max_length=200, db_index=True)

CREATE INDEX btree_idx_btreeidx_content_511ce749
    ON public.btree_idx_btreeidx USING btree
    (content COLLATE pg_catalog."default" ASC NULLS LAST)
    TABLESPACE pg_default;

CREATE INDEX btree_idx_btreeidx_content_511ce749_like
    ON public.btree_idx_btreeidx USING btree
    (content COLLATE pg_catalog."default" varchar_pattern_ops ASC NULLS LAST)
    TABLESPACE pg_default;

创建btree索引：

class BTreeIdx(models.Model):
    content = models.CharField(max_length=200)

    class Meta:
        indexes = [
            BTreeIndex(fields=['content'])
        ]

CREATE INDEX btree_idx_b_content_93bf39_btree
    ON public.btree_idx_btreeidx USING btree
    (content COLLATE pg_catalog."default" ASC NULLS LAST)
    TABLESPACE pg_default;

创建btree索引，opclass=varchar_pattern_ops：

class BTreeIdx(models.Model):
    content = models.CharField(max_length=200)

    class Meta:
        indexes = [
            BTreeIndex(name='btree_idx_like_idx', fields=['content'], opclasses=['varchar_pattern_ops'])
        ]

CREATE INDEX btree_idx_like_idx
    ON public.btree_idx_btreeidx USING btree
    (content COLLATE pg_catalog."default" varchar_pattern_ops ASC NULLS LAST)
    TABLESPACE pg_default;