Oracle - 資料表筆數、大小的計算方式

總而言之、言而總之，因為要調效能的關係，
第一步要先抓到資料筆數比較多跟Size比較大的資料表，
所以找到了一些SQL的寫法，如下：

/* 資料筆數 */
SELECT TABLE_NAME, AVG_ROW_LEN, NUM_ROWS
  FROM DBA_TABLES
  WHERE NUM_ROWS > 1000000
  ORDER BY NUM_ROWS DESC;

/* Table size */       
SELECT SEGMENT_NAME AS TABLE_NAME,
    ROUND(SUM(BYTES) /(1024*1024*1024),2) AS TABLE_SIZE_GB
  FROM USER_EXTENTS
  GROUP BY SEGMENT_NAME
  HAVING ROUND(SUM(BYTES) /(1024*1024*1024),2) > 0.5
  ORDER BY ROUND(SUM(BYTES) /(1024*1024*1024),2) DESC;

/* Data size */
SELECT TABLE_NAME, AVG_ROW_LEN, NUM_ROWS,
    ROUND (AVG_ROW_LEN * NUM_ROWS /(1024*1024*1024),2) AS DATA_SIZE_GB
  FROM DBA_TABLES  
  WHERE ROUND(AVG_ROW_LEN * NUM_ROWS /(1024*1024*1024),2) > 0.1
  ORDER BY ROUND(AVG_ROW_LEN * NUM_ROWS /(1024*1024*1024),2) DESC;

有聽過不太會寫PL/SQL，然後要來調效能的八卦嗎？