SELECT 
  cscart_bm_blocks.block_id, 
  cscart_bm_blocks_content.content 
FROM 
  cscart_bm_blocks 
  JOIN cscart_bm_blocks_content ON cscart_bm_blocks_content.block_id = cscart_bm_blocks.block_id 
  JOIN cscart_bm_blocks_descriptions ON cscart_bm_blocks_descriptions.block_id = cscart_bm_blocks.block_id 
WHERE 
  cscart_bm_blocks.company_id = 9572 
  AND cscart_bm_blocks_descriptions.name = "Register"

Query time 0.01126

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_bm_blocks",
      "access_type": "ALL",
      "possible_keys": ["PRIMARY"],
      "rows": 3237,
      "filtered": 100,
      "attached_condition": "cscart_bm_blocks.company_id = 9572"
    },
    "table": {
      "table_name": "cscart_bm_blocks_descriptions",
      "access_type": "ref",
      "possible_keys": ["PRIMARY"],
      "key": "PRIMARY",
      "key_length": "4",
      "used_key_parts": ["block_id"],
      "ref": ["staging2_wesave_com.cscart_bm_blocks.block_id"],
      "rows": 1,
      "filtered": 100,
      "attached_condition": "cscart_bm_blocks_descriptions.`name` = 'Register'"
    },
    "table": {
      "table_name": "cscart_bm_blocks_content",
      "access_type": "ref",
      "possible_keys": ["PRIMARY"],
      "key": "PRIMARY",
      "key_length": "4",
      "used_key_parts": ["block_id"],
      "ref": ["staging2_wesave_com.cscart_bm_blocks.block_id"],
      "rows": 38,
      "filtered": 100
    }
  }
}